Apparatus, methods, and systems for multi-primary display or projection

ABSTRACT

An apparatus, methods, and systems for multi-color projection or display for video or lighting applications. One aspect of the present invention comprises an algorithm for utilizing at least four primary light sources to represent a projected pixel color. The algorithm and associated system can be applied to both a natively monochromatic light source or traditional light sources filtered for their colored components. The algorithm can be used for either color sequential or parallel modes of operation. The algorithm takes input pixel data represented in a universal color coordinate system, performs a color transform, and disperses the results among parallel display devices or sequentially to a single device such that each pixel is presented by the combination of four or more primaries.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of and claims the benefit of priorityunder 35 U.S.C. §120 to U.S. patent application Ser. No. 11/557,861,filed Nov. 8, 2006, which claims the benefit of priority under 35 U.S.C.§119(e) U.S. Provisional Patent Application Ser. No. 60/734,701, FiledNov. 8, 2005, the benefit of priority of each of which is claimedhereby, and each of which are incorporated by reference herein in itsentirety.

I. BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates generally to methods and systems of videodisplay or projection and, in particular, to methods, apparatus, andsystems of color video signal decoding, manipulation, and display orprojection with improved color gamut and brightness. Applications of theinvention include, but are not limited to, video display or projectionfor home or commercial entertainment purposes or architectural lighting.

B. Problems in the Art

Video displays and projectors have advanced significantly in recentyears. Presently, digital methods of encoding video are beginning todominate. A variety of display and projection technologies using digitalencoding have emerged.

Existing electronic video devices can be generally divided into twogroups: direct view devices and projection devices. An example of adirect view device is a cathode ray tube (CRT). A direct view devicewill generally have a display screen composed of a plurality of RGBpixels. Each RGB pixel will be comprised of a plurality of sub-pixelelements, which most likely comprise a red sub-pixel element, a greensub-pixel element, and a blue sub-pixel element. The color image iscreated by the viewer's physiological and mental visual system, whichmentally integrates the rapidly changing and vacillating sub-pixels andtheir spatial neighbors to give a full color impression.

A projection system works differently than a direct view device. Aprojection system displays an image by projecting light on a viewingscreen or surface. Different colors of light can be created in twomanners. The first method is to sequentially project separate imagesusing only a single primary color and rapidly showing the same imagewith a second and then a third primary color. The images are flashed atsufficiently high frequency to give the human eye the impression that aspecific color has been generated. This sequential presentation reliesupon color combinations recorded by the human mind through temporalintegration of the separate primary color images. An issue with the useof the sequential method is that it takes three (or the number ofprimary colors being used to generate the image) times the number offrames to generate the same images that could be shown with a systemthat integrated multiple light sources into a single image. Theincreased frame rate further limits the time in which a pixel can bemodulated for primary color contribution control because of the fixedpixel transition time; therefore, the color resolution availabledecreases. The sequential system does have the benefit of having asimpler optic system. Examples of a sequential system are disclosed inU.S. Pat. Nos. 6,962,414 and 5,448,314 which are incorporated byreference in their entirety herein.

The second type of digital video projection system is a simultaneousdisplay system based upon the concept of projecting light of allprimaries (example: the red, green, blue primaries) simultaneously ontoa screen. The combination is then used to generate the colors perceivedby the human eye. The simultaneous (also called parallel or integrated)system integrates multiple primary light sources and provides an outputcomprised of an image in a single frame.

A variety of processes for digitally encoding a video signal anddecoding it for display or projection have been developed and arewell-known. Several approaches include using a Digital MicromirrorDevice (DMD) (a proprietary technology of Texas InstrumentsIncorporated, Dallas, Tex. USA), liquid crystal on silicon (LCoS), andliquid crystal display (LCD). Each of these technologies can be used todisplay an image in a sequential or parallel (integrated) color mode.Typically, these devices include a white light source separated intored, green, and blue illuminating components. The utilization of onlythree primary colors limits the gamut of displayable colors. The threecolor primaries are unable to effectively render colors throughout theentire color space the human eye can perceive.

By varying the amount of red, green, and blue light reflected from asurface or projected to a human eye, a limited number of colors in thevisible spectrum, as perceived by the human eye, can be approximated.

One method of encoding three primary colors for subsequent projection ofa target color is described by Lindbloom, at “RGB/XYZ Matrices.” 20 Apr.2003. 07 Nov. 2005http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html,incorporated by reference herein. Generally, this known algorithm takespixel data represented in a universal color coordinate system (e.g. XYZcolor space), performs a color transform, and parses the result amongparallel display devices or sequentially to a single device such thateach pixel is represented by the combination of three primaries.

FIG. 2A generally illustrates the basic process. A conventional videoprocessor 35 is used to encode a portion 31 of an image 30 (e.g. lightblue sky from image of yellow flowers and blue sky in FIG. 2A) byrepresenting a target color (here light blue) for a pixel 34 of theimage as a combination of red (R), green (G), and blue (B). In thisexample of FIG. 2A, the contributions of primary red and primary greenare smaller than primary blue. Thus, the output from video processor 35would encode the target color to be displayed for that pixel as havingthe indicated proportional contributions from the blue, red, and greenprimary sources (RGB values are R=65, G=105, and B=255). Thus, the colorreproduced on display device 36 would basically be as close to the lightblue of the image as possible. FIG. 2A indicates diagrammatically videoprocessor 35 could be configured to instruct sequential display of eachprimary (see reference #36 where the proportional contribution of blueis T=0, green at T=1, and red at T=2). Processor 35 could also operatethe display device in parallel mode (e.g. red 38R, green38G, blue38Bcontribution simultaneous at T=0).

The purpose of this known primary color mixing algorithm is to determinethe relative proportions of three given colored light sources, forexample Light Emitting Diodes (LEDs), required to produce a targetcolor.

a) CIE Color Space

The light emitted by each source is represented in CIE 2-degree 1931format, where x and y are the chromaticity coordinates and Y′ is thephotometric flux. The known quantities are represented as follows:

Primary Color Coordinates:

-   -   Given (x_(r),y_(r),Y_(r)′), (x_(g),y_(g),Y_(g)′),        (x_(b),y_(b),Y_(b)′)

Target Color Coordinates:

-   -   Given (X, Y, Z)

Although the sources are designated as red (sub r), green (sub g), andblue (sub b), it is important to note that other colors can besubstituted. The three color points form the triangle 11A or gamut (seeFIG. 1A) and those three coordinates, referred to as “primary colors,”can be used to create a chromaticity point that is within triangle 11A.

CIE color space is a widely used mathematical definition of color space(a color model describing the way colors can be represented by multiplecolor components). It was created in 1931 by the International StandardBody Commission Internationale De l'Eclairage (CIE). The CIE color spaceis defined by a special set of what are called imaginary primaries,which roughly correspond to red, green, and blue respectively. Thechromaticity of the imaginary primaries are the XYZ tristimulus curvesplotted at (0,1), (0,0), and (1,0) and are the same as the DCI 3.2.1.5Encoding Primaries. The primaries are imaginary as they are mathematicalcreations, meaning their chromaticity would be plotted beyond the domainof what the human eye can perceive.

The chromaticity diagram of FIG. 1A describes CIE color space 14 in xyspace. As seen in FIG. 1A, it appears as basically a closed horseshoeshape or area (see reference number 14 in FIG. 1A). The points on theborder of the horseshoe (line 10), known as a spectrum locus, and the xyvalues corresponding to dominant wavelength excitation, range fromapproximately 400 nanometers to 780 nanometers, as indicated. The CIEcolor space 14 defines the range of color, the visible spectrum, which atypical human eye can perceive. Line 12 closes the horseshoe between theextreme monochromatic excitation after the long and short wavelengths.Region 16 of the color space, at which the human eye perceives the color“white”, lies within the closed area 14. All colors discernable by humaneyes are inside the closed area 14. The closed area 14 defines the colorgamut of the eye. If excitation is monochromatic, it is placed on thehorseshoe border 10 and 12.

A triangle 11A with vertices R, G, and B has been superposed on colorspace 14 of FIG. 1A; (e.g. RGB points at REC709 standard). Vertices R,G, and B represent the position in color space 14 of primary colors Red,Green, and Blue respectively. Triangle 11A illustrates one problem withthree primary color reproduction. Only hues within triangle 11A can bereproduced with those three primaries. As can be seen in FIG. 1A, thearea of triangle 11A is but a fraction of the entire color space 14.

b) White Point

What is called in the art the white point, denoted by subscript w, isthe color that results from the full contribution of all three sources,and may not appear white to the human eye. A proportionality constant(m) is calculated for each source and then used to calculate the (x, y)coordinates of the white point. The photometric flux of the white pointis simply the sum of the flux from each source.

$\begin{matrix}{{m_{r} = \left( {Y_{r}^{\prime}/y_{r}} \right)}{m_{g} = \left( {Y_{g}^{\prime}/y_{g}} \right)}{m_{b} = \left( {Y_{b}^{\prime}/y_{b}} \right)}} & \lbrack 1\rbrack \\{{x_{w} = \frac{{x_{r}m_{r}} + {x_{g}m_{g}} + {x_{b}m_{b}}}{m_{r} + m_{g} + m_{b}}}{y_{w} = \frac{{y_{r}m_{r}} + {y_{g}m_{g}} + {y_{b}m_{b}}}{m_{r} + m_{g} + m_{b}}}{Y_{w}^{\prime} = {Y_{r}^{\prime} + Y_{g}^{\prime} + Y_{b}^{\prime}}}} & \lbrack 2\rbrack\end{matrix}$

c) Tri-Stimulus Values

The three light sources and the white point are then translated from CIE2-degree format into XYZ tri-stimulus values (see FIG. 1A, ref no. 18)using the following equations:

$\begin{matrix}{{X_{r} = {{\frac{x_{r}Y_{r}^{\prime}}{y_{r}}\mspace{20mu} Y_{r}} = {{Y_{r}^{\prime}\mspace{25mu} Z_{r}} = \frac{\left( {1 - x_{r} - y_{r}} \right)Y_{r}^{\prime}}{y_{r}}}}}{X_{g} = {{\frac{x_{g}Y_{g}^{\prime}}{y_{g}}\mspace{20mu} Y_{g}} = {{Y_{g}^{\prime}\mspace{25mu} Z_{g}} = \frac{\left( {1 - x_{g} - y_{g}} \right)Y_{g}^{\prime}}{y_{g}}}}}{X_{b} = {{\frac{x_{b}Y_{b}^{\prime}}{y_{b}}\mspace{20mu} Y_{b}} = {{Y_{b}^{\prime}\mspace{25mu} Z_{b}} = \frac{\left( {1 - x_{b} - y_{b}} \right)Y_{b}^{\prime}}{y_{b}}}}}{X_{w} = {{\frac{x_{w}Y_{w}^{\prime}}{y_{w}}\mspace{20mu} Y_{w}} = {{Y_{w}^{\prime}\mspace{25mu} Z_{w}} = \frac{\left( {1 - x_{w} - y_{w}} \right)Y_{w}^{\prime}}{y_{w}}}}}} & \lbrack 3\rbrack\end{matrix}$

d) Square Matrix

The tri-stimulus values of the three light sources can then berepresented as a square matrix. This matrix is inverted and multipliedby the white point to get an array of scaling factors (S). The scalingfactors manipulate the matrix of the primaries in order to relate to areference white point. If the desired white point is not the result ofthe full contribution of each primary color, then S_(r), S_(g), and/orS_(b) will deviate from unity. However, if the reference white is setequal to the full contribution of each primary color, then those valuesare equal to one.

In the event that the lighting system is being controlled by acommunication protocol, which indicates the desired colors in levels ofred, green, and blue, then a reference white is needed to maintain theintuitive nature that full red, green, and blue produce white. If theprotocol allows the capability of selecting a specific color coordinate,then a reference white is not needed.

$\begin{matrix}{\begin{bmatrix}S_{r} & S_{g} & S_{b}\end{bmatrix} = {{{\begin{bmatrix}X_{w} & Y_{w} & Z_{w}\end{bmatrix}\begin{bmatrix}X_{r} & Y_{r} & Z_{r} \\X_{g} & Y_{g} & Z_{g} \\X_{b} & Y_{b} & Z_{b}\end{bmatrix}}^{- 1}\lbrack M\rbrack} = {{\begin{bmatrix}{S_{r}X_{r}} & {S_{r}Y_{r}} & {S_{r}Z_{r}} \\{S_{g}X_{g}} & {S_{g}Y_{g}} & {S_{g}Z_{g}} \\{S_{b}X_{b}} & {S_{b}Y_{b}} & {S_{b}Z_{b}}\end{bmatrix}\begin{bmatrix}R & G & B\end{bmatrix}} = {\begin{bmatrix}X & Y & Z\end{bmatrix}\lbrack M\rbrack}^{- 1}}}} & \lbrack 4\rbrack\end{matrix}$

e) Transform Matrix

The scaling factors are multiplied by their respective color coordinatesin order to complete the transform matrix (M). The result of the matrixmultiplication of the transform by the desired color coordinate [X Y Z]is an array of three values [R G B]. This array represents the relativeproportions of each primary required in order to produce the desiredcolor point.

f) Duty Cycle

These values are then scaled to the domain of [0,1] by taking eachprimary and dividing it by the maximum value in the primary color array.

D _(r) =R/max(R,G,B)D _(g) =G/max(R,G,B)D _(b) =B/max(R,G,B)  [5]

The result is the required duty cycle (D), which can be implementedusing a number of modulation techniques (i.e. Pulse Width Modulation orPulse Frequency Modulation). Duty cycle is the percent of power that isapplied to the light source, which relates to the intensity. A dutycycle with more increments has a finer resolution, which leads to smoothtransitions between colors and precision adjustments for errorcorrection algorithms. The duty cycle calculation produces the brightestcombination of the primary colors required to make the target color.

The foregoing methodology of color mixing is known in the art. Itrequires substantial, but manageable, mathematical calculations tooperate. However, it is limited to three primary color mixing.

2. Simplified Form

These known three-color mixing calculations described above can bereduced algebraically to a simplified form that accounts for color spaceconversions.

If the target color is represented by (x_(C), y_(C)), the relativevalues of the three sources required to make that color are calculatedas follows:

$\begin{matrix}{{{color} = \left( {x_{c},y_{c}} \right)}{R = {- \frac{y_{r}\left\lbrack {{x_{b}\left( {y_{c} - y_{g}} \right)} + {x_{c}\left( {y_{g} - y_{b}} \right)} + {x_{g}\left( {y_{b} - y_{c}} \right)}} \right\rbrack}{y_{c} \cdot Y_{r}^{\prime} \cdot \left\lbrack {{x_{b}\left( {y_{g} - y_{r}} \right)} + {x_{g}\left( {y_{r} - y_{b}} \right)} + {x_{r}\left( {y_{b} - y_{g}} \right)}} \right\rbrack}}}{G = \frac{y_{g}\left\lbrack {{x_{b}\left( {y_{c} - y_{r}} \right)} + {x_{c}\left( {y_{r} - y_{b}} \right)} + {x_{r}\left( {y_{b} - y_{c}} \right)}} \right\rbrack}{y_{c} \cdot Y_{g}^{\prime} \cdot \left\lbrack {{x_{b}\left( {y_{g} - y_{r}} \right)} + {x_{g}\left( {y_{r} - y_{b}} \right)} + {x_{r}\left( {y_{b} - y_{g}} \right)}} \right\rbrack}}{B = \frac{y_{b}\left\lbrack {{x_{c}\left( {y_{g} - y_{r}} \right)} + {x_{g}\left( {y_{r} - y_{c}} \right)} + {x_{r}\left( {y_{c} - y_{g}} \right)}} \right\rbrack}{y_{c} \cdot Y_{b}^{\prime} \cdot \left\lbrack {{x_{b}\left( {y_{g} - y_{r}} \right)} + {x_{g}\left( {y_{r} - y_{b}} \right)} + {x_{r}\left( {y_{b} - y_{g}} \right)}} \right\rbrack}}{D_{r} = {{{R/{\max \left( {R,G,B} \right)}}\mspace{20mu} D_{g}} = {G/{\max \left( {R,G,B} \right)}}}}\mspace{20mu} {D_{b} = {B/{\max \left( {R,G,B} \right)}}}} & \lbrack 6\rbrack\end{matrix}$

Whereas in the first three-color mixing method the target color wasgiven in XYZ coordinates, this simplified method uses only xyY′coordinates. The simplified equations assume that the reference white isthe full contribution of each of the primary sources, so S_(r), S_(b),and S_(g) are all equal to one.

The above-described known algorithms demonstrate the reduction of athree-primary system and their duty cycles, given a target colorcoordinate. These algorithms have been used for color calculations ofRGB LED mixing systems.

However, in a trichromat system, there is a trade-off between maximizingthe color space, achieving saturated color, and being able to producecolors in the outlying areas of the CIE color space (such as pastels ordeep purples).

It has been recognized that if more primary colors were added to thesystem, the gamut size increases and fewer performance compromises maybe required. An advantage of a tetrachromat or pentachromat system (with4 and 5 primaries, respectively) is that the spectral content of theilluminating source renders surfaces to a quality that more closelyimitates natural daylight. However, one obstacle to calculating therelative contributions of systems beyond trichromat is that matrix M,discussed above, becomes non-square and is overdetermined. Itsinversion, which is required to calculate the required primarycontribution, is not deterministically solvable with traditionalmethods. Methods such as pseudoinverse using the Moore-Penrose Methodcould be attempted, but would provide only a least-squares fit of asampling of the final target colors desired. The inherent approximationof the pseudoinverse calculation introduces error into an already highlycomplex system. The complexities stem from many sources includingdegradation of output with time, temperature response characteristics,and manufacturing variability. The compound effect of real-worldvariation and the best-fit calculations would result in the defeat ofthe primary objective of accurate, repeatable color.

Thus, with the three-color mixing algorithms described above, theprimary values matrix cannot simply be expanded to accommodate morecolors because it then becomes an unsolvable non-square matrix. In atetrachromat or pentachromat system, the algorithm must be appliedseveral times.

U.S. Pat. No. 6,633,302 (“the '302 patent”) recognizes the limitation ongamut utilizing only three primary sources. It purports to offer animprovement over the same. The '302 patent discloses a static displaysystem that utilizes a cumbersome three-dimensional approach tointegrating at least four primaries. This cumbersome approach representsthe color space 14 in three dimensional XYZ volumes instead oftwo-dimensional CIE slices. In an attempt to streamline its process, the'302 patent discloses a lookup table and interpolation calculation forperforming the necessary conversion from target pixel color to relativecontribution of primaries. However, this approach introduces anotherform of estimation or approximation (including the interpolationcalculation) which, in turn, introduces potential inaccuracies into thecalculation of the combination of the primary sources. Thus, the '302system is an inadequate video projection system, especially in light ofthe present stringent requirements of the high definition digital cinemamarket.

Therefore, there is room for and a real need for improvement to thestate of the art. In particular, there is a need for a color mixingmethodology, which allows efficient calculation of target color in colorspace from four or more colors.

Additionally, many of the existing technologies utilize an incandescentor gas discharge light source. As is well known in the art, such lightsources have inherent variations and limitations, such as size,longevity, and durability. The broad spectrum nature of conventionallight sources limits the efficiency of saturated primary productionbecause of the filtering required. Superior display characteristics arenot solely a function of accurate color reproduction, but also of thebrightness and consistency of the light source. Therefore, there is alsoa need in the art for alternatives and improvements in light sourcesused for light projection.

II. SUMMARY OF THE INVENTION

It is therefore a primary object, feature, advantage and/or aspect ofthe present invention to provide apparatus, methods, and systems formulti-primary display or projection, which improve over the problems anddeficiencies in the art.

Further objects, features, advantages, and/or aspects of the presentinvention include apparatus, methods, or systems for multi-primarydisplay or projection and general illumination which provide one or moreof:

-   -   a. Efficient and effective color mixing to achieve target        colors.    -   b. Wide color gamut.    -   c. Enhanced color rendition and more life-like color.    -   d. High color rendering (e.g. 90+)    -   e. Accurate color and grayscale.    -   f. Excellent direct display or projection.    -   g. High efficiencies for the color white.    -   h. Consistency of color, even during dimming, and for repeated        specific colors.    -   i. Accurate and repeatable specifiable colors (e.g. 0.004 duv).    -   j. Low color separation.    -   k. Relatively low mathematical or processor overhead.    -   l. A relatively economical system.    -   m. Customizability.    -   n. Applicability to different light sources.    -   o. Applicability to different display or projection methods.    -   p. Applicability to different color encoding and decoding        techniques and protocols.    -   q. Compensation to account for source variation or degradation.    -   r. Compensation for temperature or other variables of the        display or projection system.    -   s. Low maintenance.    -   t. Long lamp life.    -   u. Robust.    -   v. Scene Adaptive Contrast Control™ that can be applied to the        entire display or particular areas of a display broken up into        zones.    -   w. Implementation of narrow spectrum emission sources in a        projection system.    -   x. Implementation of solid state emission sources in a        projection system.    -   y. A digital projection system having an optical arrangement of        multi-primaries constructed with a minimum focus length between        the source and the projection lens.    -   z. Efficient thermal management of high lumen density light        sources.

These and other objects, features, advantages, and/or aspects of thepresent invention will become apparent with reference to thespecification and claims herein.

One aspect of the present invention comprises an algorithm for utilizingat least four primary light sources to represent a target color. Thealgorithm and associated system can be applied to both a nativelymonochromatic light source or traditional light sources filtered fortheir colored components. The algorithm can be used for either colorsequential or parallel modes of operation. The algorithm takes inputpixel data represented in a universal color coordinate system, performsa color transform, and disperses the results among parallel displaydevices or sequentially to a single device such that each pixel isrepresented by the combination of four or more primaries. The moreprimaries, the more points of color that can be created in color space.The result is wider gamut, more accurate, life-like, purer colors. Also,in projection, higher pixel brightness is possible because more lightcan be put into producing the output of a pixel, so the colors arebrighter and more vivid. The more primaries used for the target color,the brighter the color will be.

Another aspect of the invention comprises the optional use of a closedloop optical feedback algorithm to account, correct, or compensate forvariation of the primary light sources and an optical path. The feedbackalgorithm and an accompanying sensor provide a consistent referencewhite or target color. The feedback system can use an RGB or tristimuluscorrected color sensor that feeds input data into three PID(Proportional Integral Derivative) algorithms. The third PID algorithmcan perform an auto tuning function. This system can also learn andcorrect, in essentially real time, the subsequent selection of the samecolor.

Another aspect of the present invention is the implementation of narrowspectrum emission sources into a projection system. These narrowspectrum emission sources include solid state devices such as lightemitting diodes (LEDs) and lasers. The integration of LEDs or lasersinto the projection system allows for enhanced color projection.Monochromatic sources eliminate the need for filtering, thus reducingthe complexity of the optical system and providing more saturatedprimaries. LEDs and lasers also have operational lifetimes and outputmaintenance curves that far exceed conventional light sources. Solidstate light sources are receiving generous amounts of researchattention, which is reflected by the fact that their efficacy hasimproved dramatically over the past few years and is forecast tocontinue to improve. In the future, LEDs and lasers will likely exceedthe efficiency of the most advanced incandescent and gas dischargetechnology known today.

Another aspect of the present invention comprises optional contrastcontrol to provide more dynamic color display. The fast response time ofthe solid state emission source also allows for modulation of theprimary source intensity on a frame-to-frame basis to provide anelectronic Scene Adaptive Contrast Control™ that acts as a dynamic iris.The frame-to-frame control is the result of utilizing fast responseemission sources in a dynamic range improvement algorithm to enhance thecontrast ratio of projected images. A histogram analysis of grayscale ina video image determines the proportions of light and dark colors andgrayscale. Light sources projecting the image are increased or reducedin intensity to change the dynamic range of the image, depending on thatanalysis.

Another aspect of the present invention comprises thermal management ofnarrow spectrum emission light sources. The present invention utilizes aheat pipe package that physically isolates a working fluid from theoutside environment. The heat pipe package maintains a pressuredifferential across its walls, and enables heat transfers from and intothe working fluid. Movement of working fluid creates a thermodynamicsystem that moves heat from one location near the heat source to anotherlocation away from the heat source, thus enabling the compact heatsource to be spread over a larger area for improved heat dissipation.

Other aspects of the invention comprise a projection system, whichutilizes several optical arrangements to integrate the primary colorsources to produce a target pixel color. The projection system couldalso utilize dichroics to reflect/direct the lights to combine colorsand conserve etendue. The projection system allows reduction of distancebetween the sources and the projection optics for a four or more colorprojection system, to minimize light loss.

III. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a graphical representation of prior art CIE color space witha conventional, state of the art, three primary color area trianglesuperposed on it. FIG. 1B is a graphical representation of prior art CIEcolor space with a four primary color area, according to one exemplaryembodiment of the present invention, superposed on the CIE color space.

FIG. 1C is a graphical representation of prior art CIE color space witha five primary color area, according to another exemplary embodiment ofthe present invention, superposed on the CIE color space.

FIG. 2A is a diagram illustrating prior art processing and display of acolor image using three primary color sources RGB.

FIG. 2B is a diagram like FIG. 2A but illustrating, at a high level,processing and display of a color image using four or more color sourcesP₁, P₂, P₃, and P₄, according to one aspect of the present invention.

FIG. 3A is an idealized illustration of a four primary color area ofFIG. 1B of CIE color space divided into plural triangles by linesbetween vertices.

FIG. 3B is an idealized illustration of a five primary color area ofFIG. 1C of CIE color space divided into plural triangles by linesbetween vertices.

FIG. 4A is a flow chart of a color mixing algorithm according to oneexemplary embodiment and aspect of the present invention.

FIG. 4B is a block diagram of one example of an implementation of thealgorithm of FIG. 4A.

FIGS. 5A-G are illustrations of an alternative color mixing methodologysimilar to that of FIG. 4A.

FIG. 6A is a block diagram of an error correction algorithm and systemaccording to an exemplary embodiment and aspect of the presentinvention.

FIG. 6B is a software flow diagram for an implementation of the errorcorrection algorithm of FIG. 6A, showing additional optionalcompensation methods.

FIG. 7A is an RAGCB Pixel Histogram illustrating a scene, which makesuse of less than full dynamic range of a display.

FIG. 7B is a Gain Modified RAGCB Pixel Histogram of FIG. 7A, where theimage is stretched over the entire range.

FIG. 7C is a Projected RAGCB Intensity Histogram of FIG. 7B withgrayscale of the light source decreased by the reciprocal of pixel gain.

FIG. 8 is a block diagram of a Scene Adaptive Contrast Control™ orSACC™, according to an aspect of the present invention.

FIG. 9 is an illustration of an alternative concept regarding SACC™.

FIGS. 10A-D are an exemplary embodiment of a color mixing projectorutilizing five color sources with 30°/60° dichroic mirrors to create athree lens output.

FIG. 11 is an enlarged sectional view of portions of FIG. 10A.

FIG. 12 is an isolated diagrammatic view of an optional truncatedillumination optic with reflective polarizer and quarter wave retarderthat can be used for an individual LED light source.

FIG. 13A is a top plan view of a projector system using an optic systemaccording to one aspect of the present invention, in particularutilizing five different color sources with a combination of dichroicmirrors at 45° to beam path to create a combined output through a singlelens.

FIG. 13B is an elevation view taken along line 13B-13B of FIG. 13A.

FIG. 13C is a simplified isolated view of the optics of FIGS. 13A and B.

FIG. 14 is an alternative embodiment for a five color source single lensprojector.

FIGS. 15A and B are alternative views of a still further embodiment of afive color source, single lens projector using a white light sourceinput.

FIG. 16A is a flow map of an active thermal management option for solidstate light sources such as FIG. 13A.

FIG. 16B is a diagrammatic elevation view of a cold plate assembly thatcould be used with the method of FIG. 16A.

FIG. 17 is a high level block diagram of an exemplary embodiment whichincludes several different aspects according to the invention.

IV. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENTINVENTION A. Overview

For a better understanding of the aspects of the present invention,exemplary embodiments will now be described in detail. It is notintended that the present invention be limited to the describedembodiment. It is intended that the invention cover all modificationsand alterations obvious to those skilled in the art, which may beincluded within the scope of the invention and its aspects, which aredefined solely by the appended claims.

B. Color Mixing Algorithm

The algorithm takes well-known display technology and enhances theuser's experience by representing the image with more than threeprimaries. The two main advantages of a multi-primary image system are awider color gamut and brighter colors, both because more primaries areused.

FIG. 2B illustrates the exemplary embodiment. Contrary to the previouslydescribed prior art method of FIG. 2A, the exemplary embodiment of FIG.2B encodes the target color for the pixel using at least four primarycolors (here four, namely, red 38R, blue 38B, green 38G and amber 38A torepresent a pixel 34 from a maize colored tulip in the image 30). Thecolor mixing algorithm thus has more primaries to characterize thetarget color, and thus a wider gamut of color for better, more accuratecolor rendition. An example of a video encoding protocol is highdefinition multimedia interface (HDMI) video input, but the algorithm isapplicable to most, if not all, video inputs.

The algorithm also promotes uniformity of how the colors look each timethey appear. The human eye perceives subtle differences in color. Thiscan affect not only the clarity but the enjoyment of such things as TVand movie projection, and also architectural, theatrical, and otherlighting.

1. Color Mixing Algorithm Example 1 Tetrachromat System (Colors RBGA)

The color mixing algorithm of this exemplary embodiment is implementedwith the following general method steps:

-   -   1. The three (XYZ) primary color encoded video signal is        processed and color pixel array data extracted.    -   2. The color mixing algorithm transforms individual pixel data        into an array that represents four or more primaries that would        display the target color.    -   3. Primary color data is parsed to display devices or        sequentially to a single device.        -   A projected image is displayed with a larger color gamut and            more authentic color representation than an RGB system.

In a three-color system such as described in the Background of theInvention, the primaries form one triangle 11A in the CIE color space 14with vertices RGB (see FIG. 1A). In a four-color or tetrachromat systemof the present exemplary embodiment, the primaries (for example, red,amber, green, and blue) form four triangles in color space 14. Thevertices of these triangles are RAG, AGB, GBR, and BRA in FIG. 1B. FIG.3A provides an idealized representation of each of the four trianglesrelative to their vertices.

FIG. 4A is a flow chart 100 of an example of a color mixing algorithmaccording to an exemplary embodiment of the present invention. Itimplements a computed target color into a projection system thateffectively and accurately combines at least four primary light sourcesusing two-dimensional color space and matrix calculations for computingthe target color.

Contrary to state of the art three-primary systems, the algorithm 100adds one or more additional primaries for the representation of apixel's color. This technology could be applied to nativelymonochromatic sources or traditional white sources filtered for theircolored components. Furthermore, the algorithm is not dependant on aparticular display device and works with color sequential or parallelmodes of operation.

A challenge to processing four or five colors, instead of three, is theprocessing overhead of the math needed to do so. For example, with highdefinition (HD) video, approximately 124.4 million pixels a second needto be processed. Thus, the calculations for each pixel must be done inabout 8 nanoseconds (8×10⁻⁹ second). It is not commercially practical toutilize expensive and large processors for most video projectors.Therefore, the method was streamlined to reduce computing overhead.

a) Method

(1) Steps 101-103

It must first be determined whether the target color point is insideeach of the four triangles of FIG. 3A (see reference number 101 in FIG.4A). A function ƒ is used that determines whether the target point is tothe “right” or “left” of each side of triangle RAG, for example. Eachvertex has an (x, y) coordinate expressing its location. Point R has thecoordinates (x_(R),y_(R)), point A is located at (x_(A),y_(A)), andpoint G is at (x_(G),y_(G)). The target color point has the coordinates(x_(C),y_(C)). If the results of the functions are uniformly positive ornegative, the target point is inside the triangle. If the results arepositive for one or two vertices and negative for the other(s), then thepoint is outside the triangle. Equation 7 defines the calculation forthe red-amber-green (RAG) triangle of FIGS. 1B and 3A:

fRA=(y _(C) −y _(R))*(x _(A) −x _(R))−(x _(C) −x _(R))*(y _(A) −y _(R))

fGR=(y _(C) −y _(G))*(x _(R) −x _(G))−(x _(C) −x _(G))*(y _(R) −y _(G))

fAG=(y _(C) −y _(A))*(x _(G) −x _(A))−(x _(C) −x _(A))*(y _(G) −y_(A))  [7]

(2) Step 104

Equations 7 are then repeated for the remaining three triangles AGB,GBR, and BRA. If it is determined that the target point lies within aparticular triangle, the color mixing algorithm is calculated using thetriangle vertices as the three primary colors.

(3) Step 105

All of the valid primary color results are summed (in this case, allreds would be summed, all ambers, all greens, and all blues). Thisproduces the proportions of the four primary colors required to createthe target point. The duty cycles of the primaries are then calculatedin order to normalize the proportions to a 0-1 scale. Each of the fourtotal primary results is then divided by the maximum of the four values.In this example, equation 8 defines the duty cycle for red:

$\begin{matrix}{{D_{R} = {\sum\limits_{i = 1}^{k}P_{Ri}}}{{Where}\mspace{14mu} k\mspace{14mu} {is}\mspace{14mu} {the}\mspace{14mu} {number}\mspace{14mu} {of}\mspace{14mu} {triangles}\mspace{14mu} {containing}\mspace{14mu} {the}\mspace{14mu} {{target}.}}} & \lbrack 8\rbrack\end{matrix}$

Note that the method does not require an unspecified number ofiterations or a sufficient starting point in order to provide anaccurate solution. In other words, in contrast to the well knownMoore-Penrose and Newton method, feedback from the previous trianglecalculation is not required in order to determine the outcome of thenext and the system is completely solvable without the input of arepresentative sample of desired outputs. The straightforward nature ofthe method allows for the calculations to be completed within a shortperiod of time with a standard processor.

The result of algorithm 100 is a modulated output 106 that instructseach light source 108 as to its intensity for a given point in time(e.g. for either producing collectively a reference white color or forillumination using a target color, or for instructing pixel data 107 todrive display devices 109 to collectively produce a target color).

b) Apparatus

The above-described method can be implemented in conventional apparatus,which typically would include a programmable digital processor at theheart of a controller board. The light sources and a digital storagemedium could be placed on their own separate board or substrate. Datarepresenting the chromaticity characteristics and degradation profile ofthe primary light sources can be burned onto a digital storage medium(e.g. EEPROM) on the light source board, as opposed to a controllerboard. The data would be formatted such that it could be married to anycontroller board and the information would flow seamlessly into thecontroller's operational algorithm.

2. Color Mixing Algorithm Example 2 Pentachromat System (Colors RBGAC)

The above-described system can be further expanded to include fiveprimary colors. Whereas four primaries created four triangles, fiveprimaries (see FIG. 1C) form 10 triangles. FIG. 3B defines each of thevertices of the ten triangles formed in a red-amber-cyan-green-blue(RACGB) primary system.

At this point, the same procedure is followed as for a tetrachromatsystem. It is first determined whether the target point (x_(C),y_(C)) iswithin each of the ten triangles. In the generic form of theseequations, P₁, P₂, and P₃ are the vertices of the triangle being tested.Each primary has corresponding x,y coordinates in the CIE color space.

Generic Point within Triangle Test

fP ₁ P ₂=(y _(C) −y _(P) ₁ )*(x _(P) ₂ −x _(P) ₁ )−(x _(C) −x _(P) ₁)*(y _(P) ₂ −y _(P) ₁ )

fP ₃ P ₁=(y _(C) −y _(P) ₃ )*(x _(P) ₁ −x _(P) ₃ )−(x _(C) −x _(P) ₃)*(y _(P) ₁ −y _(P) ₃ )

fP ₂ P ₃=(y _(C) −y _(P) ₂ )*(x _(P) ₃ −x _(P) ₂ )−(x _(C) −x _(P) ₂)*(y _(P) ₃ −y _(P) ₂ )  [9]

The color mixing algorithm is run on each triangle that contains thetarget point. Below is the generic form of the algorithm:

Generic Color Mixing Algorithm

$\begin{matrix}{{{color} = \left( {x_{c},y_{c}} \right)}{P_{1} = \frac{y_{P_{1}}\left\lbrack {{x_{P_{3}}\left( {y_{c} - y_{P_{2}}} \right)} + {x_{c}\left( {y_{P_{2}} - y_{P_{3}}} \right)} + {x_{P_{2}}\left( {y_{P_{3}} - y_{c}} \right)}} \right\rbrack}{y_{c} \cdot Y_{P_{1}}^{\prime} \cdot \begin{bmatrix}{{x_{P_{3}}\left( {y_{P_{2}} - y_{P_{1}}} \right)} +} \\{{x_{P_{2}}\left( {y_{P_{1}} - y_{P_{3}}} \right)} + {x_{P_{1}}\left( {y_{P_{3}} - y_{P_{2}}} \right)}}\end{bmatrix}}}{P_{2} = \frac{y_{P_{2}}\left\lbrack {{x_{P_{3}}\left( {y_{c} - y_{P_{1}}} \right)} + {x_{c}\left( {y_{P_{1}} - y_{P_{3}}} \right)} + {x_{P_{1}}\left( {y_{P_{3}} - y_{c}} \right)}} \right\rbrack}{y_{c} \cdot Y_{P_{2}}^{\prime} \cdot \begin{bmatrix}{{x_{P_{3}}\left( {y_{P_{2}} - y_{P_{1}}} \right)} +} \\{{x_{P_{2}}\left( {y_{P_{1}} - y_{P_{3}}} \right)} + {x_{P_{1}}\left( {y_{P_{3}} - y_{P_{2}}} \right)}}\end{bmatrix}}}{P_{3} = \frac{y_{P_{3}}\left\lbrack {{x_{c}\left( {y_{P_{2}} - y_{P_{1}}} \right)} + {x_{P_{2}}\left( {y_{P_{1}} - y_{c}} \right)} + {x_{P_{1}}\left( {y_{c} - y_{P_{2}}} \right)}} \right\rbrack}{y_{c} \cdot Y_{P_{3}}^{\prime} \cdot \begin{bmatrix}{{x_{P_{3}}\left( {y_{P_{2}} - y_{P_{1}}} \right)} +} \\{{x_{P_{2}}\left( {y_{P_{1}} - y_{P_{3}}} \right)} + {x_{P_{1}}\left( {y_{P_{3}} - y_{P_{2}}} \right)}}\end{bmatrix}}}} & \lbrack 10\rbrack\end{matrix}$

As in a tetrachromat system, the primary color results are then summed(all reds summed, all ambers, all cyans, all greens, and all blues) toproduce the proportion of the five primaries needed to create the targetpoint. The proportions are then normalized to a 0-1 scale by dividingeach of the five primary results by the maximum of the five values. Inthe duty cycle calculation below, k is the number of trianglescontaining the target point and n is the first term in the primaryarray.

Generic Duty Cycle Calculation

$\begin{matrix}{{D_{Pn} = {\sum\limits_{i = 1}^{k}P_{ni}}}{D_{P{({n + 1})}} = {\sum\limits_{i = 1}^{k}P_{{({n + 1})}i}}}{D_{P{({n + 2})}} = {\sum\limits_{i = 1}^{k}P_{{({n + 2})}i}}}\ldots} & \lbrack 11\rbrack\end{matrix}$

In the equations above, when k=0, the sum must equal zero. Negativeresults are not summed because they are not within the triangle.

3. Color Mixing Algorithm Example 3 More than Five Colors

This color mixing system could be expanded to more than five colors, andbeyond the examples given, using the concepts described. A simpleequation calculates the number of triangles that need to be tested for agiven number of primary colors. The generic form of this equationdetermines the number of permutations of n items chosen from a group ofm items. For the purposes of color mixing, it must be determined howmany triangles (or groups of 3) are formed in an m-color system. Thetriangles are tested and the algorithm runs exactly as for tetra- andpentachromat systems.

$\begin{matrix}{{{C\left( {m,n} \right)} = \frac{m!}{{(n)!}{\left( {m - n} \right)!}}}{{C(m)} = \frac{m!}{6{\left( {m - 3} \right)!}}}} & \lbrack 12\rbrack\end{matrix}$

4. Exemplary Implementation of Color Mixing Algorithm

FIG. 4B is a block diagram illustrating one example of an implementationof a color mixing algorithm like that discussed with respect to FIG. 4A.FIGS. 5A-G illustrate additional specifics about such an implementation.

FIG. 17 is a block diagram that places the color mixing algorithm incontext of a complete multi-primary illumination system. Color mixingalgorithm 100 would receive a target color instruction 201 from inputdata and generate a lamp gain instruction 314 that would be passed tothe driver for each light source 108. In this manner, color mixingalgorithm controls the intensity of light source 108. It is to beunderstood that this arrangement would be used for each light source108. In the embodiments described herein, there are more than three(3+n) light sources that each have their color controlled by the systemof FIG. 17. The four or more light sources can be used to producecombined illumination (e.g. pure white when all the light sources arecombined or any color possible by mixing of the sources). On the otherhand, as is well known, each light source 108 could be projected througha display device 137/138 (not shown in FIG. 17, but shown in FIG. 5A)(e.g. a pixilated light valve such as LCD, LCoS, or DMD) to project astatic image or video images. Error correction (see reference numerals200 and 202), contrast control (reference numeral 300), and heatmanagement (reference numerals 942 and 943) will be discussed in latersections.

This exemplary embodiment is in the context of a high definition (HD)projector using a field programmable gate array (FPGA) chip to providevideo processing functions (see generally ref no. 120). FIGS. 4B and 5Ashow block diagrams of the same. The device could be implemented inother integrated circuits, such as an ASIC instead of FPGA. As can beappreciated, the embodiment of FIG. 5A is described in the context ofdriving LCD's, but could drive any display device.

Input video data is an HDMI compliant video stream decoded by a SiliconImage (Sunnyvale, Calif. USA) type SIL9021CTU-7 decoder chip. Inputvideo will be 1920×1080 (1080p) pixels, progressive scan, 60 Hz, 24-bitR′G′B′ or Y′CbCr video data. As further discussed, projector 120 willinclude these features:

-   -   1. Programmable Test Pattern Generation    -   2. Tri-channel programmable Gamma Correction    -   3. XYZ Color Space Conversion for increased gamut    -   4. Hardware—what is called a symbology overlay with OpenGL        graphics provided by an on-chip NIOS II processor and DDR RAM        overlay buffer. The symbology overlay is available from Digital        Design Corp., Palatine, Ill. USA. Details can be found at        http://www.digidescorp.com/products/IP/DataSheets/DDC_symbology_overlay.pdf    -   5. Multi-Primary Pixel Processor for conversion to 5-primary        colorspace    -   6. IRDA port for remote control    -   7. Interface to Flash memory for multipurpose data storage    -   8. RS-232 interface to CrystalFontz LCD display w/6 button        interface (available from CrystalFontz America, Inc., Spokane        Valley, Wash. USA).    -   9. PCI Express or PCIe core, a well known implementation of the        PCI, to allow expandability, such as custom hardware decoding        cards.    -   10. Output to display devices (here 5 LCDs).

The high definition projector (HDP) FPGA 120 will take as input a 1080p60 Hz video signal 121/122 which is sourced from an HDMI decoder IC. Itwill then perform several video processing tasks, and drive a 5-primarydisplay device projector system (ref no. 126) for projection display.

The signal processing chain includes two major blocks, what will becalled Color Space Conversion block 127 and XYZ to 5-primary conversionblock 128.

Color Space Conversion block 126 must accept 8 bit/channel 4:4:4 YCbCror R′G′B′ data or 12 bit/channel DCI X′Y′Z′ data and generate 16bit/channel XYZ data at the output. See FIG. 5B.

XYZ to 5-primary Conversion block 128 accepts the 16 bit/channel XYZ andgenerates the 12 bit/channel primary control signals. See FIG. 5C.

Incoming video from Silicon Image decoder IC 123 can be encoded with twopossible colorspaces, namely ⁷⁰⁹Y′Cb′Cr′, or Gamma Corrected RGB(R′G′B′). The pixel data will be converted to the XYZ colorspace priorto symbology overlay 139 and 5 primary conversion.

If the incoming video is already R′G′B′, this conversion is skipped. Ifthe incoming video is 8-bit ⁷⁰⁹Y′CbCr, it is first converted togamma-corrected R′G′B′ with Eq. i:

$\begin{matrix}{\begin{bmatrix}R^{\prime} \\G^{\prime} \\B^{\prime}\end{bmatrix} = {\begin{bmatrix}1 & 0 & 1.5748 \\1 & {- 0.187324} & {- 0.468124} \\1 & 1.8556 & 0\end{bmatrix} \cdot \left( {\begin{bmatrix}{{}_{}^{}{}_{}^{}} \\{Cb} \\{Cr}\end{bmatrix} - \begin{bmatrix}16 \\128 \\128\end{bmatrix}} \right)}} & \lbrack i\rbrack\end{matrix}$

Only a subset of valid ⁷⁰⁹Y′CbCr codewords fall within 0-255 values inthe R′G′B′ space after transformation—according to modeling, 75.8% ofcodewords are out of range. These values can be clipped, however the outof range data can be maintained into the XYZ space and clip the valuesthere in order to preserve maximum accuracy, since some illegal R′G′B′values may fall as legal XYZ values after the conversion process iscomplete.

Modeling indicates that the possible ranges of the R′G′B′ values are:

R′={−202 . . . 455}

G′={−83 . . . 339}

B′={−238 . . . 491}

Therefore, the R′G′B′ values can be expressed as signed 10-bit binary(s9) numbers without resorting to clipping, providing a range of +/−512.

Pixel data in the R′G′B′ space has been gamma corrected, and thiscorrection must be undone before the values can be converted into theXYZ colorspace. This conversion will be implemented in programmable lookup table (LUT) 140 to provide flexibility, and because several differenttransfer functions are in widespread use. The LUT approach also allowsnon-linear transfer functions to be expressed easily. For example, thetransfer function specified for Rec. 709 (FIG. 5D) is an exponent of0.45, with a linear segment of slope 4.5 near the black level to preventthe infinite slope a pure exponential would provide.

Conversion of Rec. 709 RGB to CIE XYZ can be accomplished with thematrix transform in Eq. ii:

$\begin{matrix}{\begin{bmatrix}X \\Y \\Z\end{bmatrix} = {\begin{bmatrix}0.412453 & 0.357580 & 0.180423 \\0.212671 & 0.715160 & 0.072169 \\0.019334 & 0.119193 & 0.950227\end{bmatrix} \cdot \begin{bmatrix}R_{709} \\G_{709} \\B_{709}\end{bmatrix}}} & \lbrack{ii}\rbrack\end{matrix}$

As described previously, the gamut of the 5-primary color space isdefined by the chromaticity coordinates of the five primaries. Thesepoints enclose the convex two dimensional space 14 of FIG. 1C.Additionally, there are ten possible triangular sub-gamuts as shown inFIGS. 3B and 5E.

The algorithm for conversion from XYZ color space to the 5-primary colorspace involves detecting which of the ten sub-gamuts the desired colorbelongs to. A conversion from XYZ to each 3-primary sub-gamut iscalculated and the results are averaged to form the conversion from XYZto 5-primary space.

In order to reduce the complexity of the hardware, as many calculationsas possible must be pre-computed. The color conversion algorithm turnsout to be fairly deterministic (it behaves predictably). One differencebetween the methodology of this exemplary embodiment and that describedwith respect to FIG. 3B, is that the gamut is divided into eleven zones,see numbers 1-11 in FIG. 5F, as opposed to the ten zones of FIG. 3B.

By determining which of the eleven zones the desired color is in, theassociated triangular sub-gamuts are determined. Consequently theconversion matrix from XYZ to 5-primary space can be pre-computed. Thedetails of this are presented below.

A given pixel P (X,Y,Z) must be located within one of the eleven5-primary gamut zones of FIG. 5F. In order to determine in which zonethe pixel resides, it must first be transformed into the two dimensionalCIE chromaticity coordinate space. The location of an incoming pixel inCIE space is determined based on the XYZ colorspace values according toEq. iii.

$\begin{matrix}{x = {{\frac{X}{X + Y + Z}\mspace{56mu} y} = \frac{Y}{X + Y + Z}}} & \lbrack{iii}\rbrack\end{matrix}$

Now that the coordinates of the pixel P(x,y) are known, we must alsoknow the coordinates of the 5 primary colors in order to locate thezones. Sample primary coordinates are listed in Table 1 below. Thesevalues will be programmable and dependent on the colors of the lamps inthe projector.

TABLE 1 xy Coordinates of Primary Colors x y R_(p) 0.6990 0.2861 Y_(p)0.5920 0.4016 G_(p) 0.2867 0.6866 C_(p) 0.0590 0.3730 B_(p) 0.15700.0213

The 5-primary gamut is subdivided into zones by five internal linesbetween the five primary points. These lines are highlighted in FIG. 5G.We will not be making a determination of whether P(x,y) is out of gamut,therefore the five outside lines will be ignored. We can determine whichzone P(x,y) resides in by determining which side of each of the internallines P(x,y) is on, and then using a LUT to determine the zone. Theprocedure is as follows:

-   -   1) Find vectors which start at the pixel P(x,y), and terminate        at each respective primary coordinate. These five vectors now        represent the bearing and distance to each of the 5 primary        points, and will be referred to as

R(x,y),Ā(x,y), G(x,y), C(x,y), B(x,y)

-   -   2) We can now calculate the Determinant (2D cross product) of        each pair of vectors corresponding to one of the five internal        lines (Eq. iv):

$\begin{matrix}{{D_{BG} = {{{\begin{matrix}{\overset{\rightarrow}{B}(x)} & {\overset{\rightarrow}{G}(x)} \\{\overset{\rightarrow}{B}(y)} & {\overset{\rightarrow}{G}(y)}\end{matrix}}\mspace{45mu} D_{BY}} = {\begin{matrix}{\overset{\rightarrow}{B}(x)} & {\overset{\rightarrow}{Y}(x)} \\{\overset{\rightarrow}{B}(y)} & {\overset{\rightarrow}{Y}(y)}\end{matrix}}}}\mspace{25mu} {D_{CR} = {{{\begin{matrix}{\overset{\rightarrow}{C}(x)} & {\overset{\rightarrow}{R}(x)} \\{\overset{\rightarrow}{C}(y)} & {\overset{\rightarrow}{R}(y)}\end{matrix}}\mspace{45mu} D_{CY}} = {\begin{matrix}{\overset{\rightarrow}{C}(x)} & {\overset{\rightarrow}{Y}(x)} \\{\overset{\rightarrow}{C}(y)} & {\overset{\rightarrow}{Y}(y)}\end{matrix}}}}{D_{GR} = {\begin{matrix}{\overset{\rightarrow}{G}(x)} & {\overset{\rightarrow}{R}(x)} \\{\overset{\rightarrow}{G}(y)} & {\overset{\rightarrow}{R}(y)}\end{matrix}}}} & \lbrack{iv}\rbrack\end{matrix}$

-   -   3) The polarity of the five resulting determinants index a        lookup table (Table 2) which provides the corresponding zone of        P(x,y).

TABLE 2 Zone Determinant Polarity Table (Det polarity) Zone D_(BG)D_(BY) D_(CR) D_(CY) D_(GR) 1 + + + + − 2 − + + + − 3 − + + + + 4 + + +− − 5 − + + − − 6 − + + − + 7 + + − − − 8 − + − − − 9 − − + − − 10 − − +− + 11 − − − − −

Once the zone has been determined, one of the eleven pre-computed colorconversion matrices is used to generate the drive signals for each ofthe primaries. The actual conversion multiplies the XYZ vector by theconversion matrix, to generate the 5 element output vector of drivesignals. This can be expressed as:

$\begin{matrix}{\begin{bmatrix}R \\A \\G \\C \\B\end{bmatrix} = {M_{k}\begin{bmatrix}X \\Y \\Z\end{bmatrix}}} & \lbrack v\rbrack\end{matrix}$

where M_(k) is a 5×3 color conversion matrix, and k is the zone in whichthis XYZ point lies.

Each of the zones of the gamut consists of an intersection of severaltriangles whose vertices are three of the five primaries. For example,referring to the zone diagram (diagram 3, below), zone 1 is anintersection of the three triangular sub-gamuts, AGC, GCB and RGC. Acomplete list of the zones with the intersecting triangles follows:

Diagram 3: 5-Primary Conversion Zones Zone Intersecting TriangularSub-gamuts 1 AGC, GCB, RGC 2 AGC, RBC, RGB 3 RAG, AGC, AGB 4 GCB. ACB.RGC 5 RGB, RAC, AGB, RGC, ACB 6 RAG, RAC, ACB 7 ACB, GCB, RCB 8 RCB,AGB, RGB 9 RGC, RAB, RGB 10 RAG, RAB, RAC 11 RAB, RGB, RCB

To compute the color conversion matrix for each zone, the inverse of the3×3 matrix made up of the XYZ primaries for each intersecting triangleis computed. These matrices are used to populate the appropriate rows ofa set of larger 5×3 matrices with the remaining matrix entries set tozero. This group of 5×3 matrices is then averaged to form the finalconversion matrix. The following example for Zone 1 illustrates thecomputation. The primaries colors are indicated by the tripleX_(p)Y_(p)Z_(p), where p refers to one of the five primaries: R, A, G,C, B.

Thus, the method uses the following two foundational steps:

-   -   a. First compute 3×3 conversion matrix for each of the three        intersecting triangles:

$\begin{matrix}{{N_{AGC} = {{\begin{bmatrix}X_{A} & Y_{A} & Z_{A} \\X_{G} & Y_{G} & Z_{G} \\X_{C} & Y_{C} & Z_{C}\end{bmatrix}^{- 1}\mspace{20mu} N_{GCB}} = \begin{bmatrix}X_{G} & Y_{G} & Z_{G} \\X_{C} & Y_{C} & Z_{C} \\X_{B} & Y_{B} & Z_{B}\end{bmatrix}^{- 1}}}{N_{RGC} = \begin{bmatrix}X_{R} & Y_{R} & Z_{R} \\X_{G} & Y_{G} & Z_{G} \\X_{C} & Y_{C} & Z_{C}\end{bmatrix}^{- 1}}} & \lbrack{vi}\rbrack\end{matrix}$

-   -   b. Place each of the 3×3 conversion matrices inside a 5×3        sub-gamut conversion matrix and pad the remaining entries with        zero. The notation N_(AGC1.2) indicates the matrix element in        row 1, column 2 of the 3×3 conversion matrix N_(AGC).

$\begin{matrix}{M_{AGC} = \begin{bmatrix}0 & 0 & 0 \\N_{{{AGC}\; 1},1} & N_{{{AGC}\; 1},2} & N_{{{AGC}\; 1},3} \\N_{{{AGC}\; 2},1} & N_{{{AGC}\; 2},2} & N_{{{AGC}\; 2},3} \\N_{{{AGC}\; 3},1} & N_{{{AGC}\; 3},2} & N_{{{AGC}\; 3},3} \\0 & 0 & 0\end{bmatrix}} & \lbrack{vii}\rbrack \\{M_{GCB} = \begin{bmatrix}0 & 0 & 0 \\0 & 0 & 0 \\N_{{{GCB}\; 1},1} & N_{{{GCB}\; 1},2} & N_{{{GCB}\; 1},3} \\N_{{{GCB}\; 2},1} & N_{{{GCB}\; 2},2} & N_{{{GCB}\; 2},3} \\N_{{{GCB}\; 3},1} & N_{{{GCB}\; 3},2} & N_{{{GCB}\; 3},3}\end{bmatrix}} & \lbrack{viii}\rbrack \\{M_{RGC} = \begin{bmatrix}N_{{{RGC}\; 1},1} & N_{{{RGC}\; 1},2} & N_{{{RGC}\; 1},3} \\0 & 0 & 0 \\N_{{{RGC}\; 2},1} & N_{{{RGC}\; 2},2} & N_{{{RGC}\; 2},3} \\N_{{{RGC}\; 3},1} & N_{{{RGC}\; 3},2} & N_{{{RGC}\; 3},3} \\0 & 0 & 0\end{bmatrix}} & \lbrack{ix}\rbrack\end{matrix}$

-   -   c. Finally, compute the element by element average of the group        of 5×3 matrices:

$\begin{matrix}{M_{1} = \frac{\left( {M_{AGC} + M_{GCB} + M_{RGC}} \right)}{3}} & \lbrack x\rbrack\end{matrix}$

A similar calculation follows for each of the eleven zones of the gamutin FIG. 5F. These can all be pre-computed and saved in tables in thehardware.

There is some flexibility in the final computation of the zone matrix.The example given above used an average of the sub-gamut conversionmatrices since this matched the computations of the original referencemodel, however, any linear combination of the matrices would be a validsolution. It may be possible to choose some other linear combinationwhich optimizes the system with respect to some performance parameter.For example, if observer metamerism is to be reduced, certaincombinations of the sub-gamut matrices may minimize the overall changeof the reproduced spectrum when crossing zone boundaries. Thiscalculation may be pre-computed as in the above example and appliedglobally. It may also be computed in real time based on the xycoordinates of each pixel. This, of course, would require furtheranalysis and hardware but does provide an option for future systemenhancements.

Details and further information regarding concepts described above canbe found at Poynton, C., Digital Video and HDTV—Algorithms andInterfaces, Morgan Kaufmann, 2003, including pg. 317 and 251,incorporated by reference herein.

5. Summary re Color Mixing Algorithms

It can therefore be seen that the exemplary embodiments of the colormixing algorithm generally involve a method of breaking up a color spaceinto square matrices so that it can be solved. The solution requires theinversion of a matrix, but this cannot be performed because each primaryis described in terms of tristimulus values (X,Y,Z) and the inclusion ofmore than three primaries would result in a matrix that is non-square.The invention discloses an algorithm that essentially breaks up thenon-square matrix into plural square matrices in order to solve thetarget color.

The result is a solution based on more colors, which provides thedescribed advantages over the state of the art.

The result also is accomplished with reasonable processing overhead andin timely fashion for pixel-by-pixel generation. A prior art attempt touse more than three colors uses computational intense algorithms thatonly approximate the solution in a “least squares” method. Our disclosedsolution is a two-dimensional color space approach that is streamlinedand without approximation, resulting in an ideal situation for highdefinition video processing.

Another area not sufficiently addressed by the state of the art isdisplay device valve response or light sourceerror correction. In thefollowing paragraphs we will disclose an optional error correctionalgorithm that accounts for time and temperature degradation.Degradation compensation is necessary for solid state devices becauseboth chromaticity and intensity are sensitive to the aforementionedvariables. In addition, component variation can be mitigated by errorcorrection.

Simplistically, the algorithm takes pixel data represented in auniversal color coordinate system, performs a color transform, andparses the result among parallel display devices or sequentially to asingle device such that each pixel is represented by the combination offour or more primaries.

Flow diagram (see generally FIG. 2B)

-   -   Video signal processed and color pixel array data extracted.    -   Algorithm transforms individual pixel data into an array that        represents four or more primaries that would display target        color.    -   Primary data parsed to display devices or sequential to a single        device.    -   Image displayed with a larger color gamut and more authentic        color representation than an RGB system.

The color mixing algorithm can be applied in a number of scenarios andapplications. One application is a video projection system, where thecolor mixing algorithm processes the incoming pixel data, based on theinput of an array of primaries and parses the data to display devices ina parallel or sequential manner. An alternate scenario of the sameapplication is the video pixel data is processed and the color mixingalgorithm is applied as previously stated; however a parallel algorithmis also applied to independently controllable illuminating primaries sothat the target combination of all illumination is a reference whitepoint. The advantage of adjusting the illuminating primaries to producea reference white is that the available dynamic range of each pixel isenhanced because generally video data is encoded with a reference white.However, this is not a required feature. A second category ofapplications is the use in general illumination. The color mixingalgorithm controls four or more sources such that their combinationproduces any range of colors within a gamut, defined by the primaries,in a static or dynamic manner. The illumination device could receivetarget color data from any number of communication protocols, notlimited to DMX 512, Ethernet, or an internal data bus.

C. Error Correction Algorithm

Optionally, what will be called an error correction algorithm can beused with the color mixing algorithm described above. Some of theadvantages of such feedback include, but are not limited to:

-   -   (a) if actual color is not quite true, it can add offset to        correct it.    -   (b) provision of consistent reference white.    -   (c) calibration in a manufacturing environment as well as        calibration at the end user's discretion.    -   (d) accounts and compensates for light source degradation.

Error correction algorithm 200 (see FIG. 6A) could be implemented insoftware or a FPGA. As shown in the context of the system block diagramof FIG. 17, a color sensor 202 could feed back sensed actual outputcolor of light source 108 to algorithm 200. Any offset between targetcolor 201 and actual sensed color from source 108 could be detected (the“error”) and algorithm 200 could adjust color mixing algorithm 100 tocompensate or correct for the same.

The fact that light sources, especially Light Emitting Diodes (LED), areinherently variable is well-known. Even though LEDs are typically sortedby bin (color and intensity), there is still significant variationwithin each bin, to the point where each LED within a given bin isunique.

In addition, a closed-loop system using optical feedback is broadlyconsidered important for consistent color control. See, e.g., Muthu,Subramanian & James Gaines.

“Red, Green and Blue LED-based White Light Source: ImplementationChallenges and Control Design.” Industry Applications Conference, 2003.38th IAS Annual Meeting (12-16 Oct. 2003). Volume 1: 515-522.Proportional Integral Derivative (PID) algorithms are widely implementedfor the compensation of variability in complex systems. See, e.g.,Wikipedia. “PID Controller.” 5 Nov. 2005. 07 Nov. 2005<http://en.wikipedia.org/wiki/PID_controller>.

The error correction algorithm according to this exemplary embodimentimplements these two commonly-known techniques (closed-loop optical feedback and PID algorithms) for non-square matrix color systems. The lackof symmetry in these systems requires a deviation from the conventionalapproach to eliminate error.

FIG. 6A illustrates the error correction algorithm 200. The algorithmwill be described with respect to the following projection system andcolor sensor.

1. Step 202

The light source 108 for a projection system could utilize five colors,namely red, amber, green, cyan, and blue LEDs from a modulated output106 (which provides a duty cycle for each source to produce a targetcolor 201) from color mixing algorithm 100 described above. A colorsensor 202 (e.g. model number TCS230 RGB from Texas AdvancedOptoelectronic Solutions, Inc. of Plano, Tex. USA.) would sense not onlyreal time feedback of color from the light source, but intensity of thelight energy from the mixed sources and produce an output signal.

2. Step 204

Data conversion 204 of the optical sensor output signal is thenaccomplished as follows. A color correction transfer matrix iscalculated for the sensor by the method described in “Sensing color withthe TAOS TCS230,” with several modifications. See Poynton, Charles.“Sensing color with the TAOS TCS230”, copyright May 17, 2005 TAOS, Inc.and available at www.taosinc.com, and incorporated by reference herein.

Specifically, the Macbeth color checker chart reflectance samples of thePoynton method referenced immediately above were replaced with theradiometric distribution of the desired combinations of the LEDs. Inaddition, the response curves of the red, green, and blue sensors werescaled such that the full contribution of all the light sources wouldresult in a measurement of one across each color channel. Finally, thereference white was set equal to illuminant E. These modifications werenecessary because optical sensor 202 is looking at the direct emissionfrom a combination of sources and not the reflectance off a surface.

Sensor 202 does not have to be RGB. For example, it can be a threechannel color corrected sensor as produced by MAZeT Electronic Designand Manufacturing Services of Jena, Germany. The color corrected sensorreduces the complexity of measuring accurate chromaticity data for thesource(s).

The color transformation matrix is used to translate the scaled datafrom the sensor into chromaticity coordinates. The information is brokeninto three parts: x, y, and the absolute magnitude of error between themeasured point and the target point.

3. Steps 205-209

The three parts of the signal from data conversion step 204 are fed intoparallel PID algorithms 206, 207, and 208, where the x and y portions(see reference number 205) are collectively used to modify the input 209to color mixing algorithm 200, and the third PID algorithm 208 is usedfor an auto-tuning function.

Algorithm 208 is tuned such that under varying conditions, the responseis smooth, consistent and time-efficient. The tuning can be accomplishedseveral ways, however the application of magnitude-of-error PID 208 toprovide tuning feedback for this exemplary embodiment is configured asfollows.

If the target chromaticity coordinate (target color SP 201 in FIG. 6A)is far away, the algorithm makes a large change to input adjustment 209.Conversely, it makes a small change if the coordinate 201 is close.

PID algorithm 206, 207, and 208 is implemented using the followinggeneric equations:

$\begin{matrix}{{{Error}\mspace{14mu} {Calculation}}{{e(k)} = \left( {{SP} - {PV}_{f}} \right)}{{Proportional}\mspace{14mu} {Action}}{{u_{p}(k)} = \left( {K_{c}*{e(k)}} \right)}{{Trapezoidal}\mspace{14mu} {Integration}}{{u_{I}(k)} = {\left( \frac{K_{C}}{T_{i}} \right)\left( {{\sum\limits_{i = 1}^{k}{\left\lbrack \frac{{e(i)} + {e\left( {i - 1} \right)}}{2} \right\rbrack \Delta \; t{Partial}\mspace{14mu} {Derivative}\mspace{14mu} {Action}{u_{D}(k)}}} = {{{- K_{c}}\frac{T_{d}}{\Delta_{t}}\left( {{{PV}_{f}(k)} - {{PV}_{f}\left( {k - 1} \right)}} \right){PID}\mspace{14mu} {Output}{u(k)}} = {{{{u_{P}(k)} + {u_{I}(k)} + {{u_{D}(k)}{Output}\mspace{14mu} {Limiting}{If}\mspace{14mu} {u(k)}}} \geq {u_{\max}\mspace{14mu} {then}\mspace{14mu} {u(k)}}} = {{{u_{\max}{and}{if}\mspace{14mu} {u(k)}} \leq {u_{\min}\mspace{14mu} {then}\mspace{14mu} {u(k)}}} = u_{\min}}}}} \right.}}} & \lbrack 13\rbrack \\{{u(t)} = {K_{c}\left\lbrack {\left( {{SP} - {PV}} \right) + {\frac{1}{T_{i}}{\int_{0}^{t}{\left( {{SP} - {PV}} \right)\ {t}}}} - {T_{d}\frac{{PV}_{f}}{t}}} \right\rbrack}} & \;\end{matrix}$

In the above equations, SP is the set point or target color 201 andsignal PV is the measured point or feedback from the optical sensor. Thegeneric form is applied to x_(C), y_(C), and abs separately, with theexception that error is calculated for abs as follows:

$\begin{matrix}{{{e\_ abs}(K)} = \sqrt{\left( {{SP}_{xc} - {PV}_{xc}} \right)^{2} + \left( {{SP}_{yc} - {PV}_{yc}} \right)^{2}}} & \lbrack 14\rbrack\end{matrix}$

The product of the tuning function (u_abs) and optional scaling factor(g_(a)) determines the value of K_(C), known as gain.

K _(C) =u _(—) abs*g _(a)  [15]

The output of the x and y coordinate PID 205, u_x_(C) and u_y_(C)respectively, modify an input 209 to color mixing algorithm 100, asshown in FIG. 6A. Color mixing algorithm 100 can be of the type of theexamples of color mixing algorithms discussed above, or other types.

4. Optional Control

An additional layer of control could be employed such that PIDalgorithms 206, 207, and 208 could learn from previous convergence on asolution. The fundamental principle could be implemented by a simplememorization of past target points and required inputs or by devising atransformation matrix that is continually refined to represent thebridge between the assumed color coordinates of the sources and themeasurement of their combinations. A system that learns could use thisdata to reduce convergence time in subsequent selections of the samecolor (when the memorization technique is used) or any color (when thetransformation matrix technique is used).

5. Summary of Error Correction Algorithm

As stated previously, the closed-loop optical feedback in combinationwith the PID implementation, in which the optical sensor channels andsystem primaries are mismatched, is adapted to correct systems with morethan three primaries using a low-cost optical sensor and features aself-tuning and learning function. The invention offers a customizable,high-quality, and consistent lighting tool for various markets, notlimited to entertainment, architectural, film, and studio lighting.

Implementation of the closed-loop optical feedback system, using an RGBcolor or tristimulus value corrected sensor, includes the following:

-   -   (a) calibration of the color sensor.    -   (b) feeding the color sensor data into three parallel PID        algorithms.    -   (c) the third PID algorithm provides an auto tuning function.    -   (d) the system can learn correction trends and use this data to        reduce conversion time in subsequent selections of the same        color.    -   (e) provide consistent reference white;    -   (f) characterize the response of each display device given a        particular color and digital grayscale setting.    -   (g) calibration in a manufacturing environment and any time the        end-user wishes to recalibrate their projection or illumination        system.        The PID algorithm looks at error in three ways:

(1) Proportionally—from a magnitude standpoint; how far is themeasurement from desired point.

(2) Integrally—continually sums the magnitude of error.

(3) Derivatively—how fast is the algorithm approaching a point based onslope.

Answering the question: Is the algorithm over- or under-compensating?

It is important to note that there are many ways to tune a PID algorithmor apply a self tuning method. The one given is for example and isparticularly suited for situations where the point of interest is faraway and a large change is made, and if the point of interest is close,a small change is made.

The algorithm allows for correction for temperature, time, and colordegradation. As LEDs heat up their dominant wavelength shifts towardred; when they cool, it shifts toward blue. There are intensity changeswith temperature, especially the AlInGaP (Aluminum Indium GalliumPhosphide), which is amber and red. InGaN (Indium Gallium Nitride),which is blues, cyans, and greens tend to be more stable, however theirvariation is significant enough to warrant the need for correction.

Thus, this closed loop feedback compensates for time and temperaturedegradation and component variation. The method corrects for transientchanges (e.g. temperature changes) or long term changes (e.g. lumendepreciation over thousands of hours).

It can also make the LED manufacturing process shorter and cheaper. Themanufacturer would not need the best manufacturing data with this systemof correction, which would save time and resources. The manufacturer andcustomers could be content with just bin numbers. Manufacturingcalibration could include the following process. A set of red LEDs couldbe turned on. A spectrometer measurement is taken. That primary orchromaticity data and intensity data is then fed into the videoprocessor board so it knows the basic operating parameters of the LEDs,at least during initial operation.

FIG. 6B is a flow chart diagram 350 indicating a specific implementationof a general illumination LED controller for DMX-512 digital multiplexedsignals communications protocol. DMX-512 is a well-known communicationsstandard, which covers digital multiplexed signals. It is the mostcommon communications standard used by lighting and related stageequipment.

The DMX-512 signals are processed by RS-485 Transceiver 353 into DMXvalues 356 which can be processed by color mixing algorithm 357. Colormixing algorithm 357 can be that described earlier with respect to FIGS.1-5, which outputs instructions to duty cycle modulator 364 to, in turn,control current source 365 which then controls LED engine 366 togenerate the appropriate average intensity for the given LED lightsource (not shown). The current source could be based on a switch modepower supply topology so that it has high efficiency (i.e. the HV9910available from Supertex, Sunnyvale Calif.).

However, system 350 provides correction for offset between theinstructed target value based on the received DMX values and the actualcolor generated from the LED light source. Color sensor 202 generatesfrequency values of R, G, and B signals representative of actual sensedcolors of the LED being powered by LED engine 366. The RGB frequenciessignals from TAOS 230 color sensor 202 are measured by a color channelselectable frequency counter 351. The RGB values are converted to x,ycolor coordinates using principles of step 204 to create a duty cyclecompensation signal at reference numeral 359. The compensation signal isfed back to duty cycle modulator 364 and adjusts the duty cycle ofelectrical power to LED engine 366 to compensate for any offset or errorbetween the instructed color and the sensed color. As previouslydescribed, this can produce more accurate and consistent color bycompensating for whatever might affect the actual produced color todiffer from the instructed color.

FIG. 9 also shows additional possible optional compensation. Similar tothe color sensor and compensation, an appropriate temperature sensor 354(e.g. thermocouple or thermistor) could be operatively placed relativeto the light source and its analog voltage signal, representing sensedoperating temperature of the light source, can be converted to digital(reference number 355) and processed in six channel voltage totemperature algorithm 360 to convert voltage to temperature. Data 363about the operating characteristics of the LED being used could bestored in EEPROM 362. Such information could include information abouthow color output of the LED varies with operating temperature. Sensedoperating temperature could be compared to the data and a compensationinstruction could be generated (see reference numeral 361) which, inturn, could be used to generate a compensation signal from 361 whichwould be fed back into duty cycle modulator 364 to adjust or compensatefor operating characteristics as programmed into 362. Variations incolor or output from the LED can be compensated for to promote accurateand consistent color regardless of operating temperature. It is wellknown that, e.g., the color and output of LEDs vary with operatingtemperature. Note also that FIG. 6B indicates other operating criteriaabout the particular light source could be stored in EEPROM 362 and usedto correct or compensate the light source output. This would allow themanufacturer of the lighting system to build-in, at the factory,compensation sub-systems for many of the reasons there can be variationin color or light output from light sources. For example, some lightsources experience lumen depreciation over operating life. Lumendepreciation could result in substantial reduction in light output fromthe light source, which could materially affect performance of thelighting system. There could be other color, photometric, or electricalcharacteristics for which compensation could essentially be programmedinto the system.

Thus, as indicated at FIG. 6B, error correction can adjust, correct orcompensate for such variances or conditions. In a theatre light, colorcompensation could ensure an accurate, consistent true white output.

D. Narrow Spectrum Sources

The projection system discussed above that implements the aforementionedcolor mixing and error correction algorithms can optionally andbeneficially use narrow spectrum emission sources as primary lightsources. For example, FIGS. 13A-C disclose an exemplary embodimenthaving an arrangement of primary light sources 812 arranged and alignedwith dichroics 814. These narrow spectrum sources 812 can be lightemitting diodes (LEDs) of the type that collectively can producehundreds of lumens. One example is the OSTAR LED from Osram OptoSemiconductor, Munich, Germany. Other narrow spectrum devices couldinclude, but are not limited to, lasers or a filtered wide spectrumsource such as xenon or UHP lamps currently sold on the market.

They can be modulated in intensity on a frame-to-frame basis to providean “electronic dynamic iris”, as opposed to state of the art mechanicaliris. The fast response of the source in accompaniment with a dynamicrange improvement algorithm, Scene Adaptive Contrast Control™ (SACC™),discussed in detail later, provide enhanced contrast ratio of the imagebased on the relative intensity of the frame itself.

The prior art tends to use multi-chromatic sources with filters. Thisinvolves complexity and cost to those systems, and does not provide theadvantages of narrow spectrum sources.

Solid-state, narrow band emission sources have advantages of longexpected operating life, individual primary component modulation for thecorrection of the reference white point, and the ability forframe-to-frame modulation to produce enhanced image contrast.

For example, the use of LEDs, a solid state source, as the primarysource has the inherent advantage of allowing individual primarycomponent modulation for the correction of the projected color. The LEDalso allows for the necessary frame-to-frame modulation necessary toimplement what is called Scene Adaptive Contrast Control™ or SACC™,which will be discussed in more detail below. The LED devices also havea greater life expectancy, higher lumen maintenance, and low ultraviolet(UV) and infrared (IR) which contribute to display device degradation.Additionally, LEDs have no hazardous material (i.e. mercury).

Generally speaking, conventional prior art projector bulbs have a lifeexpectancy of 1,000-3,000 hours. An LED of the type contemplated hereintypically will last 50,000 hours before the source has degraded by 30%in intensity. LEDs, when properly controlled, typically have these typesof advantages:

-   -   (a) High color rendering (90+)    -   (b) Repeatable specifiable color (0.004 duv)    -   (c) Precision target illumination    -   (d) Low maintenance, long life (70% lumen maintenance after 50K        hours)    -   (e) Explosion proof, high vibration resistance, withstands        extreme temperatures.    -   (f) Color or specific wavelengths    -   (g) High repeatability

Although not required for the color mixing and error correctionalgorithms described, they can advantageously be used with them.

E. Scene Adaptive Contrast Control™ (SACC™)

Contrast is one of the most important aspects of video. SACC™ looks at ahistogram analysis of the grayscale in a video image to determine ifthere are a lot of bright or dark colors and if the image in itsentirety is dark or bright. Depending on that analysis, the lightsource(s) are turned up or down in intensity to change the dynamic rangeof the image.

As indicated at the block diagram of FIG. 17, SACC™ contrast controlalgorithm 300 (see FIG. 8) could be implemented in software or a FPGAand adjust lamp gain 314 before it is sent to the light source driver.

When there is a bright light source, the human eye will adapt to thatlight source. If an image is produced that is mostly dark, and then animage of the sun is produced, if one takes the same level of light, theimage will look washed out because the eye adjusts to that light source.So if it is sensed that the current frame is a “dark” frame, the lightsource is turned down a little and the apparent contrast ratio goes upsignificantly.

The challenge is modulating the light source at a speed to change thesource's intensity with every frame. Even though typical video framerates are between 24 and 60 frames per second, the light source needs tobe adjusted significantly faster than the reciprocal of the frame rate;otherwise, there would be a lag between the scene and the illuminationlevel. Standard gas discharge lamps make this essentially impossible.However, LEDs respond on the order of 40 nanoseconds, so it is possibleto change LED intensity in the first few moments of any given frame.Thus, SACC™ closely can match the relative brightness of an image andeffectively change the dynamic range of that image or series of imagesframe-by-frame. Essentially this comprises dynamic lamp correction or adynamic iris. An entire frame is reviewed. A comparison of darkness andbrightness is made. Intensity is scaled down.

A state of the art approach to contrast control is to use essentially amechanical iris to control the amount of light. However, this isrelatively slow, so it may not be effective. Also, there is a very realincrease in the probability the device will fail over time. SACC isessentially an “electronic iris” which is high enough speed to adjustframe-by-frame, and is also robust over long operating times.

The use of the previous described primary color mixing algorithm andcorrective algorithm allow for what will be called Scene AdaptiveContrast Control™ (SACC™). SACC™ is the process of dynamicallymodulating the backlight of a display device based on the scenestatistics. This process improves the dynamic contrast by matching thebrightness of the backlight with the brightest pixels in the scene.

The underlying intent of SACC™ is to assure that the full dynamic rangeof the display device is being utilized for all scenes. The diagram ofFIG. 7A shows a histogram of a scene which makes use of less than thefull dynamic range of the display (see curve 322 relative to “saturationvalue” and “maximum pixel value”). By adjusting the gain of the digitalpixel values, the image can be modified so that the histogram stretchesover the entire range, as shown in FIG. 7B (see curve 324). Then, inorder to maintain the same projected scene brightness, the intensity ofthe lamp or light source(s) is/are decreased by the reciprocal of thepixel gain. The resulting intensity histogram (see curve 326) is asshown in FIG. 7C.

By comparing FIG. 7A to FIG. 7C, it would appear that no effectivechange has resulted. There is no difference in overall intensity;however, by scaling the pixel values, there is an increase in grayscaleresolution. This means that details in dark or shadowed areas which areindistinguishable without SACC™ become visible with SACC™. In otherwords, SACC™ decreases the brightness of the light source(s) to increasethe contrast ratio (dynamic range) of the projection. This can basicallyincrease the “life-like” qualities of a projected image.

Implementation of SACC™ is reasonably straight-forward. A high levelblock diagram 300 is shown in FIG. 8. The incoming five primary data,RAGCB, (collectively referred to by reference number 302) is from theoutput of the XYZ to RAGCB conversion of the color mixing algorithmpreviously described. This data has been processed to clip negativevalues and the pixel values have a large number of fractional bits belowthe binary point due to the matrix multiply. A predetermined number ofmost significant bits of these values are passed to the Histogram andGain Calculation path (see path through components 304, 306, and 308 ofFIG. 8). Since the algorithm only cares about the higher portions of thedynamic range, the maximum value (see reference number 304) of RAGCB ispassed to Histogram (ref no. 306). The purpose of Histogram 306 is todetermine how much of the dynamic range is actually used by the currentframe. A “Threshold value” is provided to the Histogram block. Thisvalue is set so that a small number of bright outliers do not influencethe selection of the Saturation Value or “S” that is passed to gaincomputation 308 which controls lamp gain with lamp gain signal “G_(L)”and pixel gain with pixel gain signal “G_(P)”.

Once per frame, histogram 306 is analyzed. The frame can be processed inreal time or from a frame buffer. This is accomplished by summing thehistogram bin values starting at the highest bin value. When this sumexceeds Threshold, the corresponding bin is selected as the SaturationValue, S. The Pixel Gain, G_(p) is calculated from S and the MaximumPixel Value, M with:

$\begin{matrix}{G_{P} = \frac{M}{S}} & \lbrack 16\rbrack\end{matrix}$

The Lamp Gain, G₁ is the reciprocal of this:

$\begin{matrix}{G_{l} = \frac{S}{M}} & \lbrack 17\rbrack\end{matrix}$

For a moderately sized histogram, these calculations could be handledwith a pre-calculated look-up table. The SACC™ algorithm can beimplemented within the main processor.

The SACC™ is useful for such things as the following:

-   -   (a) a Scene Adaptive Contrast Control™ that can be applied to        the entire display or particular areas of a display broken up        into zones, wherein each zone could be illuminated by single or        multiple LEDs and each modulated accordingly to the grayscale        histogram analysis of each zone.    -   (b) the ability to characterize the response of each display        device given a particular color and digital grayscale setting.    -   (c) the ability to modulate the intensity of the light sources        on a frame to frame basis by providing an electronic dynamic        iris.    -   (d) integration of a fast response source with a dynamic range        improvement algorithm that provides enhanced contrast ratio of        the image based on the relative intensity of the frame itself.

Essentially, SACC™ lowers the intensity of the light sources for darkpixels and raises intensity for bright pixels for improved contrastratio or dynamic range, and can do so with reasonable computationaloverhead and at a complementary speed to most, if not all, video refreshrates.

FIG. 9 illustrates a variation on SACC™. A single frame image 371 withrelatively bright portion(s) 372 (e.g. image of the sun) and relativelydark portion(s) 373 (e.g. a dark cloud) can be broken up into aplurality of histogram regions (in FIG. 9 the number of regions N istwelve. As can be seen histogram region 375 (corresponding to imageportion 372—the sun) would have a much brighter intensity value thanhistogram region 376 (corresponding to image portion 373—the cloud). Thehistogram component 374 would direct N (here twelve) brightness levelsto an illumination source and optics array 378 (having a correspondingnumber N of illumination sources, each with an associated optics array).The SACC™ algorithm would control brightness levels of each lightsource/optic of array 378, which in turn illuminates the image ondisplay device 379.

F. Active Temperature Control

Solid state narrow band emission sources have the inherent advantages oflong life, individual primary component modulation for the correction ofthe reference white point, and the ability for frame-to-frame modulationthat allows an enhanced image contrast. However, these benefits come atthe cost of high thermal density and sensitivity. Solid state sourcesrequire a thermal management system which maintains the sources at aconstant temperature, below their maximum junction temperature, forrepeatability and reliability of the system.

Incandescent light sources radiate approximately 85% of their heat. Incontrast, LEDs radiate about 15% and conduct about 85%. Because an LEDis a solid state semiconductor, it has a maximum junction temperature(e.g. 125 degrees C.) and a sensitivity to heat.

LEDs of the type used in system 800 of FIG. 13A dissipate about 120watts and have a junction to case thermal resistance of 0.67 degree perwatt. This means the LED board cannot get hotter than 44.6 degrees C.The ambient environment surrounding the light source typically is 25degrees C. Therefore, the temperature delta between source and ambientis small, which poses a challenge. Additionally, the semiconductor diearea is approximately 1 square centimeter, which rivals the powerdensities of state of the art computer processors.

Typical prior art heat management uses heat sinks 816 (see, e.g., FIG.10A or FIG. 13A) and/or movement of air. However, this can beinsufficient for systems such as a video projection system 800 of FIG.13A. A typical heat sink for an LED of the type used herein would haveto maintain a temperature only several degrees higher than the ambienttemperature, which is not practical. Heat sinks are generally consideredpassive heat dissipating devices and are insufficient for precisetemperature control. Active temperature control is beneficial tomaintain a certain temperature to minimize sensitivity to heat.

Thus, a primary concern with the use of LEDs, or other light sourceswith similar heat issues, is the thermal management of the heatgenerated by each primary source. The management of the heat is criticalfor the reliability and repeatability of the digital video projectionsystem.

An exemplary embodiment of a heat management system 900 that could beused with, for example, each LED, laser, or other light source isillustrated at FIGS. 16A and B. Generally, heat management system 900uses (a) a heat spreading assembly (with optional active control) toeffectively spread and transfer heat from each of the 5-primary colorsources (for example, Blue, Cyan, Red, Amber, and Green) (see FIG. 16B)and (b) cold plate technology and a circulating cooling fluid/radiatorsystem to radiate heat from the heat spreading assembly to the air.Active thermal management components can be added to the system tocontrol the temperature more precisely.

The projector power supply, which powers the primary sources and controlcircuitry, can be cooled by cold plate technology as well.

The block diagram of FIG. 17 illustrates that one example of active heatmanagement could be use of a thermoelectric cooler or TEC 942 that usesoperating temperature feedback from the light source to adjust theamount of heat transferred away from light source 108. The TEC 942 canbe controlled by a programmable TEC controller 943, or controller 943could be controlled by the system processor.

1. Heat Spreading from Each Heat Source

FIG. 16B illustrates a heat spreading assembly for each light source orlight engine 930. Light source 930 is a solid state device, comprising asemiconductor die or array 931 operatively mounted on a substrate 932.Also, a truncated illumination optic 933 extends from light source 931opposite substrate 932. Optic can be of the type illustrated in moredetail in FIG. 12.

During operation, heat from the relatively small die/array 931 tends toconcentrate at location 991 of substrate 932. The heat spreadingassembly, discussed below, spreads this concentrated heat over a muchlarger surface, which then can more effectively be managed.

a) Heat Pipe or Vapor Chamber 938

Heat management employs a commercially available flat heat pipe orplanar vapor chamber 938. In application, heat pipe 938 would beoperatively associated with each LED light source. Heat pipe 938essentially wicks heat from its area of abutment 990 to the heat sourceto a separate, larger region. FIG. 16B is roughly representative of thephysical scale of the light source and the heat spreading assembly.

The principles of heat pipes are well-known. An example of such a flatheat pipe can be found at www.Thermacore.com and commercially availableflat heat pipe products are available from Thermacore International,Inc. of Lancaster, Pa. USA. A description of how these commerciallyavailable systems work can be found athttp://www.thermacore-europe.com/catalogue/category.asp?cat=1. Also see,Conroy, C. T., et al., “Multiple Flat Plate Evaporator Loop Heat PipeDemonstration”, at http://www.tthresearch.com/MultiEvapLHPBettis.pdf,which is incorporated by reference herein, for general principles ofheat pipes.

Planar heat pipe or vapor chamber 938 comprises a sealed copper tubeencasing a low pressure fluid solution. The upper side of heat pipe 938is larger in perimeter dimensions than light source substrate 932 and isthermally connected to light source substrate 932 with low melt alloy(LMA) layer 936. LMAs are a type of thermal interface material (TIM).Specifically, LMAs are metals that become liquid at relatively lowtemperature. In this case, the melting temperature is selected to behigher than the normal operating condition of the light source, so thatthe LMA is a solid throughout the entire range of the semiconductordevice's operation. However, the melting temperature is below themaximum junction temperature of the solid state light source. The LMAprovides a high thermal conductivity path between the typical LEDpackage (including the LED 931, its circuit and circuit board, and itstypical heat dissipating substrate 932). Further details about LMAs canbe found at U.S. Pat. No. 7,078,109, incorporated by reference herein.

The vapor chamber package 938 basically employs a sealed hollowcontainer that physically isolates the working fluid from the outsideenvironment. The vapor chamber or heat pipe package maintains a pressuredifferential across its walls, and enables heat transfers from and intothe working fluid. Inside the heat pipe, the container is lined with aporous structure. The primary purpose of the porous structure is togenerate capillary pressure to transport the working fluid from acondenser to an evaporator. As the temperature rises at the heat source,the heat pipe assembly boils the working fluid, turning it into a vapor.As the evaporating fluid fills the hollow heat pipe, it spreadsthroughout the assembly towards the cooler or lower side of the heatpipe. The working fluid then condenses at the cooler lower side, givingoff heat in the process. As the working fluid cools, it condenses, andis sucked back to the evaporating section along the porous section ofthe heat pipe assembly. This movement of working fluid creates athermodynamic system that moves heat from one location near the heatsource to another location away from the heat source, thus spreading thehigh density heat at the solid state light source over a larger area.The working fluid of the heat pipe assembly provides a high thermalconduction path between the solid-state light source and the oppositeside of the heat pipe.

Alternative heat spreaders are possible. An example is a metal matrixcomposite (MMC) heat sink, an example of which can be found athttp://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=8955,incorporated by reference herein. Another example is graphite laminatedto a high conductivity substrate with or without thermal vias.Alternatively, a layer or plate of solid material with good thermalconductivity could be used. Examples of material would be copper anddiamond (natural or synthetic). Most materials with good thermalconductivity can function as a heat spreader. However, heat plate 938 ismuch more efficient. The lower the operating junction temperature of theLED source, the brighter it is.

2. TEC

Heat pipe 938 provides high thermal conductivity in the xy plane foroptimal heat spreading. The dispersed heat is then pumped through asolid-state heat pump, otherwise known as a thermoelectric cooler or“TEC” 942 (see commercially available TECs from Melcor Corporation,Trenton, N.J. USA at www.Melcor.com), which uses the Peltier effect toforce a temperature difference and move a specific amount of heat fromone side of the device to the other.

TEC 942 is essentially a heat pump and a thermal control device. It isnot passive like a heat sink, but rather can be termed active. It issandwiched between heat pipe 938 and cold plate 916 by thermal interfacematerial or layers (TIM) 940 and 944, as shown in FIG. 16B. TIM 940 and944 can be thermal pads or film (phase change materials), or thermalgrease or paste. They would provide effective heat transference as eventwo nearly flat surfaces usually have small gaps between them. Such TIMsare commercially available from a variety of sources, e.g. Dow-Corning,Midland, Mich. USA and Laird Technologies, Cleveland, Ohio USA.

Because the TEC is a p-n junction semiconductor, when current is forcedacross it during operation, it forces a temperature difference. One sidegets relatively cool; one side relatively hot. TEC 942 uses the Peltiereffect to force a temperature difference between the p-n junction of thesemi-conductor material of TEC 942. The cool side is brought intoabutment with planar heat pipe 938, the hot side into abutment with thecold plate 916. The bigger the temperature gradient is between the fluidsource used to cool the object and the object itself, the more effectivethe system.

TEC 944 can be adjustably controlled by controller 943 (e.g. model LTC1923 Thermoelectric Cooler Controller from Linear Technology Corp.,Milpitas, Calif. USA). Instructions can be communicated from a processor(e.g. white point board processor). TEC 944 can use a PID algorithm,with feedback from thermistor 945 placed at the heat source, and beconfigured to actively control temperature to 38 degrees C. on the frontside and a much hotter 40, 50, or even 70 degrees C. on the back. Thisinvolves tens of degrees of thermal difference, so the active thermalmanagement system is much more effective. Also, thermistor 945 at lightsource 930 can feed back operating temperature to controller 943, andcontroller 943 can be programmed to maintain a relatively constanttemperature for light source 930.

3. Cold Plates 916, Cooling Fluid, and Radiator System As shown in FIG.16B, TEC 942 for each light source is thermally interfaced with a coldplate 916. The power supply also has a cold plate assembly, seereference number 916PS.

Each cold plate assembly is essentially an enclosed chamber 922 with aninlet/outlet port. As shown in FIG. 16B, a plurality of bosses or pins923 extend downward from the upper interior surface of cold plate 916 toincrease total surface area of that surface (in comparison to it beingflat). The pin geometry and positioning is optimized to the desiredthermal resistance between the fluid and the heat source at a given flowrate. Tubing 920 brings cooling fluid in and out of chamber 922.

Cooling fluid 950 is circulated by pump 914 through fluid circuit 920tubing or fluid conduit to and from radiator 906. A cool fluid reservoir912 can store a quantity of cooling fluid (e.g. 0.5 liter). The tubes920 carry fluids past each cold plate 916, thus drawing heat away fromthem. The working fluid can be water, fluorinert, liquid metal, or anyother fluid that is optimized for the desired heat capacity,conductivity, turbulence through the fluid loop (heat circuit), heatload, and flow rate of the system. The heat circuit consists of the coldplates 916, pump 914, and a radiator 906. Radiator 906 is a conventionaldesign, having a plurality of heat radiating surfaces.

Fans 903A and B (low noise and relatively low speed) move ambient air901, filtered through air filter 902, through air duct 904 and over andthru radiator 906. Heat extracted from the five light sources and powersupply by the cold plates, and moved to radiator 906 by heated fluidsection 922 of the fluid circuit, is removed from radiator 906 by thepressurized air 905. A heated air output 907 can be directed into theambient air around the projector.

As can be appreciated, the specific components to create the heatmanagement system 900 of FIGS. 16A and B can vary according to need. Byusing cold plates, relatively substantial quantities of heat can beeffectively removed from the light sources and dispersed into the air.

As shown in FIG. 16A, the cooling fluid circuit 920 has two pathways,one flowing in series through cold plates 916 for the amber, red, cyan,and blue color sources, and the other in series through the cold platesfor the color green and for the power source. This arrangement isselected for the following reasons. First, the green LED light sourcehas the highest power rating, and the amber and red LEDs are mostsensitive to heat, so cooling fluid 950 is first presented to them. Onthe other hand, the power supply is less sensitive, as are cyan and blueLEDs, so cooling fluid is presented to them after passing through coldplates for the others. Second, minimization of the number of parallelflow paths allows for better flow rates of the cooling fluid 950 forheat transfer than if each cooling plate was in parallel.

The two flow paths will be relatively balanced in flow rate. Pump 914(e.g. model DDC-2 from Laing Thermotech, Inc., Chula Vista, Calif. USA)was selected because it is relatively low noise and relatively small insize. It can pump around 400 liters/hour.

The fluid circuit would be sealed. Tubing 920 is of robust, durablenon-permeable material. If material like Norprene® (Saint Gobain ofCourbevoie, France) is used, it would be clamped over nipples atjunctions to the components. If copper, it could be soldered. Pressuretests using vacuum could be conducted to remove all air bubbles andconfirm the fluid circuit is sealed.

4. Assembly of Heat Management System The assembly of FIG. 16B can beconstructed as follows. The combination of cold plate 916, TEC 942, heatpipe 938, and light source 930 would be stacked vertically, with lowmelt alloy 936, and TIM 940 and 944 in place where indicated. Amechanical force would be applied to compress the combination of parts,and it would be heated to above the melt point for low melt alloy 936.This procedure would make the TIM layers and low melt alloy layer asthin as possible, which promotes better heat transfer (generally thermalresistance decreases with decrease in bond line thickness). The low meltalloy 936 would also change phase to a liquid and flow into even tinygaps between the lower surface of light source substrate 932 and theupper surface of heat pipe 938. The subassembly would then be cooled andalloy 936 would change state back to a solid. It would essentiallysolder substrate 932 to heat pipe 938. The alloy 936 would essentiallybe “married” to the heat pipe 938 and be metal-to-metal contact.

5. Operating Features

Noise is a substantial issue with video projectors, particularly forhome entertainment purposes. The reduction of noise in the projectionsystem is a beneficial result that increases the user's enjoyment of aprojected video display or illumination system. Using heat managementsystem 900 allows use of a low speed fan(s) 903 (or to run fans at lowerspeeds), so that the projector is relatively quiet. It is believed thattypically fan(s) 903 could be operated in a manner where noise would notexceed around 30 decibels, which is the level of noise in a recordingstudio. Pump 914 can also be low noise.

Optionally, temperature of cooling fluid 950 could be monitored by anappropriate sensor. If temperature exceeded a certain level, appropriatecircuitry could reduce power, increase fan speed, or shut the wholeprojector down as an automatic failsafe.

Optionally, temperature of heated output air 907 exiting from radiator906 could be measured (e.g. with a thermistor). Speed of fans 903 couldbe increased or total power consumption reduced as the air temperaturerises. Additionally, fans 903 could be four-wire fans for adjustment ofspeed. A tachometer could measure fan speed and a pulse width modulatedor other electrical signal could adjust fan speed. If the tachometerdoes not sense any rotation of a fan, it can assume the fan hasmalfunctioned and cause the other fan to increase speed.

Two fans 903 are used in the embodiment of FIG. 16A to spread air flowover a larger area. This allows use of a radiator with a relativelylarge surface area.

The thermal management system 900 promotes the following:

-   -   (a) low melt alloys that provide a high thermal conductivity        path between a light source and a heat dissipating substrate.    -   (b) flat heat pipes to provide high thermal conductivity in the        XY plane for optimal heat distribution.    -   (c) a video projection system that uses a solid state heat        pump/thermal electric cooler to force a temperature difference        across the substrate that moves heat from one side of the device        to the other.    -   (d) a digital video projection system having a fluid filled heat        circuit that circulates the fluid to cool the light source.    -   (e) a thermal management system that allows for precise and        consistent control of the temperature of the solid-state light        source, enabling consistent chromaticity and intensity.

Thermal management system 900 can be scaled and configured as needed forsystem 800. Mathematical modeling and empirical testing can establishthe needed configuration. At a minimum, system 900 should not allowtemperature to exceed the junction temperature for the semi-conductorlight source.

Thermal management system 900 is designed to be long-lasting anddurable. LEDs have normal operating lives on the order of 50K hours.TECs of the type described can have mean time before failure (MTBF) onthe order of 200K hours. Heat pipes of the type described have, as apractical matter, unlimited life. Although use of water or other fluidswith a commercial projection system is counter-intuitive, system 900 issealed, robust, and should outlast the LEDs.

It is believed that active temperature management may extend the MTBF ofLEDs.

The exemplary embodiment thermal management system described above isbut one form heat management could take. It is to be understood,however, that it does not preclude the use of the more traditionaldevices such as fans and heat sinks.

Some alternatives for heat management include forced air convection, ora fan over a heat sink.

G. Optic System

The method of integrating more than three primary colors to produce atarget color, as discussed above, can be used for a number of variousapplications and can be implemented with a number of optic systems.

1. Three Lens Projector

FIGS. 10A-D and 11 disclose a three projection lens system projector 870that has three lenses 872, 874, and 876 that project light and mix itonto a viewing surface. Each projection lens is mounted at the end of anoptical chamber 873, 874, and 877, respectively (see also FIG. 11).Though having only three projection lenses 872, 874, and 876, projectionsystem uses five color sources (e.g. LEDs or some other high intensitylight sources—not shown), each illuminates a display device 880, 882,884, 886, and 888, respectively. The display devices control the amountof light transmitted to and projected by the corresponding lenses 872,874, or 876.

FIG. 11 shows basically a horizontal cross-section of each chamber 873,875, and 877 and illustrates how five light sources are combined intothree projection lenses. Each lens 872, 874, and 876 has an associatedchamber 873, 875, or 877. Two of the chambers, 873 and 877 have twoprimary light sources (here LCD displays 880 and 886 for chamber 873,and displays 884 and 888 for chamber 877). Chamber 875 has only onedisplay 882. The arrangement of FIGS. 10A-D and 11 allows placement ofall light source/display combinations relatively close to its lens whichreduces light loss.

The triple projection lens system allows for green to be very close inspectral content to cyan or amber without interference. The advantage ofhaving the spectral content of green close to another primary componentis that it allows for increased brightness on the screen withoutincreasing etendue beyond the current value. It is preferable that thegreen light source have its own projection lens because the greenwavelength is the most predominant color when generating white light.

The other two chambers combine two colors. A dichroic intentionallyplaced at an angle to the nominal light direction from bothsources)(30°/60°, has coatings that only allow the color of lightintended to pass. The 30°-60° angle is selected for the most efficienttransmission and reflection of light. As is well known, it is moreefficient than 45°-45°. A 20-70° could be even more efficient, but maybe less adaptable to this projection application.

-   -   The use of three projection lenses keeps distances of display        devices to their respective projection lens very close. All five        colors are grouped into three pieces, so effectively system 870        has the same advantages as a RGB projector as far as LCD        distance to the lens. In other words, note how LCD 886 and 888        can be placed quite near its respective lens 872 and 876. This        allows for a relatively short light path length for each. This        not only allows for a more compact projector, but also for less        light loss, which tends to occur with increasing distance. Thus,        two additional colors can be added to projector 870. The color        mixing algorithm 100 could be used for increased color gamut.        Higher screen and white luminance can be created by projecting        only green through one of the three lenses because of green's        disproportionately large contribution to the reference white.        Even though the remaining four colors must be combined in pairs        relative to the other two projection lenses, the light paths are        kept short to avoid light loss by use of a single dichroic.

FIGS. 10A-D show the relative locations of the display device, the LEDor other solid state light source, with truncated optic 840 as shown inFIG. 12, as well as a thermal management system 900, as shown anddescribed with respect to FIGS. 16A and B.

2. Single Projection Lens, Five Color Systems

FIGS. 13A-C illustrate another five color projector 800. But note thateach of the five different LED light sources 812 are positioned ingenerally the same plane, and at different orientations to the opticalpath through a single optic 850. Projector 800 uses one projection lensas opposed to the three of projector 870 of FIGS. 10A-C and 11.Similarly, projector 800 uses monochromatic solid state narrow bandemission sources (e.g. LEDs or LED arrays) which are controlled inintensity by color mixing algorithm 100.

In this embodiment, dichroics 814 are used to combine the five sources812 into one. The five sources could be any narrow spectrum light. Anexample of the specific colors could be as follows:

Color Wavelength (nm) Blue less than 470 Cyan 470 to 510 Green 510 to550 Amber 550 and 615 Red greater than 615

These ranges given are for specific dichroic designs and could bemodified to incorporate other primary colors or change the wavelengthcomposition of the primary components.

Dichroic mirrors 814 are placed along the optical paths for each lightsource as shown. FIG. 13C indicates the combination of each light sourceas two pairs B/C and A/R of sources 812 are first preliminarilycombined, then G (green) is combined with B/C, and finally BCG iscombined with RA at the output.

A conventional 45° split dichroics system is used in FIGS. 13A-C. Eachdichroic comprises a plate of light transmitting glass with thin filmsof dielectrics deposited thereon. Each layer is nanometers thick. Eachthickness creates essentially a resonant chamber. Whenever a wavelengthof light enters that chamber, when it is equal to typically four timesthe thickness, the layer becomes resonant. By well known methods, thethin films or layers are built up on a glass plate so they reflectcertain wavelengths (that is colors), and thus transmit otherwavelengths (colors) (e.g. reflect blue, transmit red or visa versa).For additional explanation of the functionality and composition ofdichroic mirrors, seehttp://www.rp-photonics.com/dielectric_mirrors.html, incorporated byreference herein.

The configuration of FIGS. 13A-C serves two main purposes for projectionsystem 800. First, all sources 812 are brought as close as possible toprojection optics 850. Light is diverging, so the farther away thedisplay device or source is from the projection optic, the larger theprojection optic has to be in order to collect all the light.Conversely, the shortest light path loses the least amount of light. Itis, of course, beneficial to maintain the greatest amount of light inthe projection system.

Second, it conserves etendue. The method of combining all five sourceswith the dichroics “tricks” the system into “seeing” one LED array whenreally there are five. This is extremely useful in projecting light. Allthe light ends up being at the same point with the colors combined.

FIG. 14 illustrates an alternative embodiment of a five color, singlelens projection system but with 30°-60° dichroics.

3. Single White Light Source, Five Color Projection System

FIG. 15A is a view of an alternative embodiment of a five color, singlelens projection system 860 with 30°-60° dichroics, and FIG. 15B has 45°dichroics. Note, however, the primary difference of the optic system isthat a single white light source 861 is the input.

A first set of dichroics 862 a-d are used as beam splitters to breakwhite light 861 up into five colors B, C, G, A, R. A second set ofdichroics or mirrors 866 a-d re-direct the monochromatic light intocorresponding display devices 864B, 864C, 864G, 864A, and 864R. A thirdset of dichroics 868 a-d recombines the light from the display devicesinto the single output. All optical paths could be made equal. Thedichroics would be selected to pass/reflect the appropriate wavelengthsof light.

4. Truncated Illumination Optic

FIG. 12 illustrates an embodiment of an optic 840 that could be usedwith display devices requiring polarized light (for example, an LCD)described herein to increase efficiency of illumination of the display.

As shown, an LED source 842 emits light which is directed by reflector841 into truncated illumination optic 843 which has total internalreflection (TIR). A quarter-wave retarder 844 and a reflective polarizer845 are operatively positioned at the output end of optic 843.

As illustrated in FIG. 12, light beam 846 from source 842 would firsttravel part way down optic 843 (see portion 846 a) and strike theinterior of optic 843. By TIR, it reflects at an angle and travels tothe output end of optic 843 (portion 846 b). It passes throughquarter-wave retarder 844 and strikes reflective polarizer 845.

A portion of light beam 846 (portion 846 e) would be polarized bypolarizer 845, and would project from optic 843 as indicated toilluminate the display with polarized light, such as LCD 880 of FIG.10A.

A portion 846 c, not allowed to pass by polarizer 845, would bereflected and travel back through retarder 844 into optic 843, bounce byTIR off of an interior surface of optic 843 (ray portion 846 d), strikereflector 841, and “recycle” back along paths 846 a and b. Becauseportion 846C passes twice through quarter wave retarder 844, it wouldessentially be converted to a polarization that would pass throughpolarizer 845 the second time.

This arrangement provides for what might be called polarizationrecycling. Polarization-recycling techniques have been proposed toincrease the efficiency of illumination of LCD panels. For properoperation, illumination with polarized light is necessary, but a typicallamp generates unpolarized light. Passing the unpolarized source lightthrough a polarizer on the way to the LCD panel wastes the half of thelight that is in the undesired polarization. To increase the efficiencyof illumination (could be on the order of 20 percent), system 840essentially “recycles” the otherwise wasted light, converting theundesired polarization to the desired one.

Details regarding polarization recycling can be found at a variety ofsources, including http://www.nasatech.com/Briefs/June01/NPO20824.html,incorporated by reference herein.

H. Options and Alternatives

As can be fully appreciated by those of skill in the art, the exemplaryembodiments are but specific examples of some of the forms the inventioncan take. Variations and alternatives to the exemplary embodiments arepossible. Variations obvious to those skilled in the art will thereforebe included within the scope of the invention, which is defined solelyby the appended claims.

For example, the exemplary embodiments primarily discuss examples usingLED light sources. However, other sources are possible. In fact almostany source is possible. For example, a white bulb could be used as asource. Dichroics could be used to break the white source up into thefour or more colors, and then recombine them with the color mixingalgorithm. The same thing could be done with a white LED. Xenon and UHPlamps are some other examples of sources.

The combination of the conventional solid state light source technologyand disclosed thermal management and optical systems allows a videoprojector to produce more than 250 lumens incident on the viewingscreen. In order to view content at a reasonable size and ambient lightlevel, this level of illumination or greater is required.

Furthermore, specific examples are given for mixing four and fivecolors. The invention can also be implemented for greater than fivesources.

Also, the examples primarily discuss use with projectors, such as videoprojectors. However, aspects of the invention can be used in the contextof direct view displays of video. Also, as briefly mentioned, aspects ofthe invention can be used in light projectors for lighting applications,as opposed to projecting or displaying video content. Entertainment,stage, film, architectural, and studio lighting, as well as underwaterlighting are other examples. TV, home theatre, commercial movie theatre,and dynamic or static content based signage, handheld devices (iPod,cell phone, laptop), console or computer video games, and monitors areother possible applications.

Additionally, certain aspects of the invention can be used independentlyof other aspects. For example, FIG. 17 illustrates how color mixingalgorithm 100, error correction algorithm 200, SACC™ contrast control300, and active heat management 942 can be used together. It is to beunderstood, however, that color mixing algorithm can be usedindependently of these other aspects for a variety of application solong as more than three colors are mixed. Error correction algorithm 200could be used with any light source and is not limited to four or morelight source systems. Similarly, SACC™ contrast control is not limitedto use with algorithms 100 and/or 200, nor is active heat management.

1. An apparatus for generating a target color comprising: a first, asecond, a third, and at least a fourth light source, wherein each lightsource has light source chromaticity coordinates in the CIE color spaceunique to each source; a processor configured to: calculate a gamut areain the CIE color space defined by the light source chromaticitycoordinates, wherein each light source provides a vertex of the gamutarea, the gamut area includes sub gamut areas formed using vertices ofthe gamut area, and each of the sub gamut areas overlap with at leastone of other of the sub gamut areas; determine which of the overlappingsub gamut areas contain the CIE color space chromaticity coordinates ofthe target color, use square matrices to perform a color mixingalgorithm to calculate a solution for each of the overlapping sub gamutareas that contain the CIE color space chromaticity coordinates of thetarget color; use the calculated solution for each of the overlappingsub gamut areas that contain the coordinates of the target color tocalculate proportional values of each primary necessary to generate thetarget light for each valid sub gamut area; and provide an outputcontrol signal for providing the target color using the calculatedproportional values.
 2. The apparatus of claim 1, wherein the lightsources are configured to adjust an intensity of light to generate thetarget color in response to the control signal.
 3. The apparatus ofclaim 1, further comprising a display device configured to adjust pixeldata for the target color in response to the control signal.
 4. Theapparatus of claim 1, wherein the light sources are solid state lightsources.
 5. The apparatus of claim 4, wherein the solid state lightsources are light emitting diodes.
 6. The apparatus of claim 4, whereinthe solid state light sources are lasers.
 7. The apparatus of claim 1,wherein the apparatus includes a fifth light source.
 8. The apparatus ofclaim 7, wherein the light sources are amber, red, blue, cyan and greensolid state light sources.
 9. The apparatus of claim 1, wherein eachlight source provides a primary color for the color mixing algorithm,and the processor is configured to use the proportional values toproduce pixel data for a display device for each primary color.
 10. Theapparatus of claim 9, wherein the pixel data is presented sequentiallyto each display device.
 11. The apparatus of claim 9, wherein the pixeldata is presented in parallel to each display device.
 12. The apparatusof claim 9, further comprising illuminating or backlighting each displaydevice with at least one of the light sources to project or present animage.
 13. The apparatus of claim 1, wherein the processor is configuredto use the proportional values to provide the output control signal todrive a light source for each primary color to compositely produce areference white color.
 14. The apparatus of claim 13, wherein each lightsource illuminates a display device.
 15. The apparatus of claim 1,further comprising: a light source driver for each light sourceconfigured to drive each light source according to the calculatedproportional values in response to the control signal; and an opticsystem configured to project light from the light source.
 16. Theapparatus of claim 1, further comprising at least a chamber to directlight emitted from the light sources to form a beam path.
 17. Theapparatus of claim 1, further comprising multiple chambers, each chamberconfigured to direct light to form a beam path.
 18. The apparatus ofclaim 17, wherein there are a first, a second, and a third chamber. 19.The apparatus of claim 18, wherein the three chambers arranged in amulti-primary projector are constructed to allow a minimum focal lengthbetween the sources and the projection lens.
 20. The apparatus of claim19, wherein the minimum focal length is less than 200 mm.
 21. Theapparatus of claim 19, wherein the minimum focal length is less than 120mm wherein the beam paths of the light sources are merged using a splitdichroic.
 22. The apparatus of claim 1, further comprising a thermalmanagement system for each light sources.
 23. The apparatus of claim 22,wherein the thermal management system comprises a heat spreader.
 24. Theapparatus of claim 23, further comprising a thermal interface betweenthe light source and the heat spreader.
 25. The apparatus of claim 24,wherein the thermal interface comprises low melt alloy.
 26. Theapparatus of claim 23, wherein the heat spreader comprises a planarvapor chamber.
 27. The apparatus of claim 22, wherein the thermalmanagement system comprises a thermoelectric cooler.
 28. The apparatusof claim 1, wherein the processor includes a closed-loop feedback systemutilizing an algorithm to provide a consistent reference white.
 29. Theapparatus of claim 28, wherein the closed-loop feedback systemcharacterizes the response of each light source or display device givena particular target color.
 30. The apparatus of claim 28, wherein theclosed-loop feedback system characterizes the response of each lightsource or display device given a digital grayscale setting.
 31. Theapparatus of claim 28, wherein the closed-loop feedback system isconfigured to be calibrated in a manufacturing environment.
 32. Theapparatus of claim 28, wherein the closed-loop feedback system isconfigured to be recalibrated by an end-user.
 33. The apparatus of claim1, wherein the light sources are solid state light sources, and thesolid state light sources are narrow-spectrum emission sources.
 34. Theapparatus of claim 1, wherein the light sources are solid state lightsources configured to modulate intensity on a frame-to-frame basis. 35.The apparatus of claim 34, wherein the controller is configured tomodulate intensity using a dynamic range improvement algorithm thatprovides enhanced contrast ratio based on both an image and a relativeintensity of the frame itself.